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VOL. I. 



T?U right of Translation w reserved. 



The aim of tluB work is to set forth the general truths of 
Biology, as illustrative of, and as interpreted by, the laws 
of Evolution : the special truths being introduced only so 
far as is needful for elucidation of the general truths. 

For aid in executing it, I owe many thanks to Prof. 
Huxley and Dr Hooker. They have supplied me with in- 
formation where my own was deficient; and in looking 
through the proof-sheets, have pointed out errors of detail 
into which I had fallen. By having kindly rendered me 
this valuable assistance, they must not, however, be held 
committed to any of the enunciated doctrines that are not 
among the recognized truths of Biology. 

The successive instalments which compose this volume, 
were issued to the subscribers at the following dates: — 
No. 7 (pp. 1—80) in January, 1863; No. 8 (pp. 81—160) 
in April, 1863; No. 9 (pp. 161—240) in July, 1863; No. 
10 (pp. 241—320) in January, 1864; No. 11 (pp. 321—400) 
in May, 1864; and No. 12 (pp. 401—476) in October, 1864, 

London, September 29th, 1864. 




I. — OBGAITIC MATTEB ' . . . . . . • . 3 





CUM8TAN0ES . . . . . . . . 72 


COBBESPONDENCE . • • . . . 82 

VII. — THE SCOPE OF BIOLOGY . . . . . . 94 




II. — ^DEVELOPMENT • . • • 

. . 133 


. . 163 

IV. — ^WASTE AND BEPAIB . . . . 

.. 1G9 























§ 1. Of. the four chief elements which, in yarions com- 
binations, make up living bodies, three are gaseous. While 
carbon is known only as a solid, oxygen, hydrogen, and 
nitrogen are known only in the aeriform state. Under 
pressures great enough to reduce them almost to the density 
of liquids these elements haye still defied all efforts to liquefy 
them. There is a certain significance in this. When we 
remember how those re-distributions of Matter and Motion 
which constitute Evolution, structural and functional, imply 
motions in the units that are re-distributed ; we shall see a 
probable meaning in the fact that organic bodies, which 
exhibit the phenomena of Evolution in so high a degree, are 
mainly composed of ultimate units having extreme mobility. 
The properties of substances, though destroyed to sense by 
combination, are not destroyed in reality : it follows from the 
persistence of force, that the properties of a compoimd are 
resultants of the properties of its components — resultants in 
which the properties of the components are severally in full 
action, though greatly obscured by each other. One of the 
leading properties of each substance is its degree of molecular 
mobility; and its degree of molecular mobility more or 
less sensibly affects the molecular mobilities of the various 
compounds into which it enters. Hence we may infer some 
relation between the gaseous form of three out of the four 

1 ♦ 


chief organic elements, and that comparative readiness dis- 
played by organic matters to imdergo those changes in the 
arrangement of parts which we call development, and those 
transformations of motion which we call function. 

Considering them chemically instead of physically, it is 
to be remarked that three out of these four main components 
of organic matter, have affinities which are narrow in their 
range and low in their intensity. Hydrogen combines with 
comparatively few other elements ; and such chemical energy 
as it does show, is scarcely at all shown within the limits of 
the organic temperatures. Of carbon it may similarly be said 
that it is totally inert at ordinaiy heats ; that the number of 
substances with which it unites is not great ; and that in 
most cases its tendency to unite with them is but feeble. 
Lastly, this chemical indifference is shown in the highest 
degree by nitrogen — an element which, as we shall here- 
after see, plays the leading part in organic changes. 

Among the organic elements, including under the title 
not only the four chief ones, but also the less conspicuous re- 
mainder, that capability of assuming different states, called 
allotropism, is frequent. Carbon presents itself in the three 
imlike conditions of diamond, graphite, and charcoal. Under 
certain circumstances, oxygen takes on the form in which it 
is called ozone. Sulphur and phosphorus (both, in small 
proportions, essential constituents of organic matter) have 
allotropic modifications. Silicon, too, is allotropic ; while 
its oxide, silica, which is an indispensable constituent of 
many lower organisms, exhibits the analogue of allotropism 
—isomerism. And even of the iron which plays an active 
part in higher organisms, and a passive part in some lower 
ones, it may be said that though not known to be itself allo- 
tropic, yet isomerism characterizes those compounds of it that 
are found in living bodies. Allotropism being interpretable 
as some change of molecular arrangement, this frequency 
of its occurrence among the components of organic matter, 
is significant as implying a further kind of molecular mobility. 


One more fact, that is here of great interest for us, must 
be set down. These four elements of which organisms are 
ahnost wholly composed, present us with certain extreme 
antitheses. While between two of them we have an unsur- 
passed contrast in chemical activity ; between one of them 
and the other three, we haye an unsurpassed contrast in 
molecular mobility. While carbon, by successfully resisting 
fusion and yolatilization at the highest temperatures that can 
be produced, shows us a degree of atomic cohesion greater 
than that of any other known element, hydrogen, oxygen, and 
nitrogen, show the least atomic cohesion of all elements. And 
while oxygen displays, alike in the range and intensity of its 
affinities, a chemical energy exceeding that of any other 
substance (unless fluorine be considered an exception), nitrogen 
displays the greatest chemical inactivity. Now on calling to 
mind one of the general truths arrived at when analyzing 
the process of Evolution, the probable significance of this 
double difference will be seen. It was shown (First Princijylea^ 
§ 123) that, other things equal, unlike units are more easily 
separated by incident forces than like units are — that an inci- 
dent force falling on units that are but little dissimilar does 
not readily segregate them; but that it readily segregates 
them if they are widely dissimilar. Thus, these two extreme 
contrasts, the one between physical mobilities, and the other 
between chemical activities, fulfil, in the highest degree, a 
certain further condition to facility of differentiation and in- 

§ 2. Among the binary combinations of these four chief 
organic elements, we find a molecular mobility much less 
than that of these elements themselves ; at the same time 
that it is much greater than that of binary compounds in 
general. Of the two products formed by the union 

of oxygen with carbon, the first, called carbonic oxide, which 
contains one atom of carbon to one of oxygen (expressed by 
the symbol G 0), is an incondensible gas ; and the second 


carbonic acid, containing an additional atom of oxygen (C 0,) 
assumes a liquid form only imder a pressure of nearly forty 
atmosplieres. The several compounds of oxygen with 

nitrogen, present us with an instructive gradation. Protoxide 
of nitrogen, which contains one atom of each element (N 0), 
is a gas condensible only under a pressure of some fifty at- 
mospheres ; deutoxide of nitrogen (N 0,) is a gas hitherto 
uncondensed (the molecular mobility remaining undiminished 
in consequence of the volume of the united gases remaining 
unchanged) ; nitrous acid (N O3) is gaseous at ordinary 
temperatures, but condenses into a very volatile liquid at the 
zero of Fahrenheit ; peroxide of nitrogen (N O4) is gaseous at 
71", liquid between that and 16% and becomes solid at a tem- 
perature below this ; while nitric acid (N O5) may be obtained 
in crystals which melt at 86* and boil at 113". In this 
series we see, though not with complete uniformity, a de- 
crease of molecular mobility as the weights of the compound 
molecules are increased. The hydro-carbons illus- 

trate the same general truth stiU better. One series of them 
will suiRce. Marsh gas (C, H4) is permanently gaseous. 
Olefiant gas (C4 H4) may be liquefied by pressure. Oil 
gas, which is identical with olefiant gas in the proportions 
of its constituents but has double the atomic weight, (Cg H,), 
becomes liquid without pressure at the zero of Fahrenheit 
Amylene (GiJELio) ^ ^ liquid which boils to 102*. And the suc- 
cessively higher multiples, caproylene (Ci, Hi,), caprylene 
(Cie Hia), elaene (Gig Hig) and paramylene (Cjo Hjo), are liquid* 
which boil respectively at 102% 13P, 267% 230% and 329% 
Cetylene (C,, H„) is a liquid which boils at 627" ; while pa- 
raffine (C^ H^) and mylene (0,0 H^,) are solids. Only 

one compound of hydrogen with nitrogen has been obtained 
in a free state — ^ammonia (Hg N) ; and this, which is gaseous, 
is liquefiable by pressure, or by reducing its temperature to 
— 40" F. In cyanogen, which is composed of nitro- 

gen and carbon (N C,), we have a gas that becomes liquid at 
a pressure of four atmospheres and solid at — 30" F. And^ in 


paracyanogen, formed of the same proportions of these ele^ 
ments in higher multiples (N, Ce), we have a solid which does 
not fuse or Tolatib'ze at ordinary temperatures. Lastly^ 

in the most important member of this group, water, (H 
or else as many chemists now think H, O,) we have a com- 
pound of two incondensible gases which assumes both tha 
fluid state and the solid state within ordinary ranges of 
temperature ; while its molecular mobUity is still such that 
its fluid or solid masses are continually passing into the form 
of vapour, though not with great rapidity until the temper- 
ature is raised to 212**.* 

Considering them chemically, it is to be remarked of 
these binary compounds of the four chief organic elements, 
that they are, on the average, less stable than binary com- 
pounds in general. Water, carbonic oxide, and carbonic 
acid, are, it is true, di£Bicult to decompose. But omitting 
these, the usual strength of union among the elements of the 
above-named substances is low considering the simplicity 

♦ This immenae loss of molecular mobility which oxygen and hydrogen un- 
dergo on uniting to form water — a loss far greater than that seen in other binary 
compounds of analogous composition — suggests the conclusion that the atom of 
water is a multiple atom. Thinking that if this conclusion be true, some eridenoe 
of the fact must be afforded by the heat-absorbing power of aqueous yapour, 
I lately 'put the question to Prof. Tyndall, whether it resulted from his ex- 
periments that the yapour of water absorbs more heat than the supposed sim- 
plicity of its atom would lead him to expect. I learned from him that it Am an 
ezcessiye absorbent power — an absorbent power more like that of the complex* 
atomed yapours than like that of the simple-atomed yapours — an absorbent 
power that therefore harmonizes with the supposition that its atom is a multiple 
one. Besides this anomalous loss of molecular mobility and this anomalous heat- 
absorbing power, there are other facts which countenance the supposition. The 
unparalleled eyolution of heat during the combination of oxygen and hydrogen is 
one. Another is that exceptional property which water possesses, of beginning to 
expand when its temperature is lowered below 40" ; since this exceptional property 
is explicable only on the assumption of some change of molecular arrangement— a 
change which is comprehensible if the molecules are multiple ones. And yet a 
further confirmatory fact is the ability of water to assume a colloid condition ; for 
as this implies a capacity in its atoms for aggregating into high multiples, it 
suggests, by analogy with known cases, that they have a capacity for aggregating 
into lower multiple!. 


of the substances. With the exception of acetylene, the 
yarious hydro-carbons are not producible by directly com- 
bining their elements ; and the elements of most of them are 
readily separated by heat without the aid of any antagonistic 
affinity. Nitrogen and hydrogen do not unite with each 
other immediately; and the ammonia which results from 
their mediate union, though it resists heat, yields to the 
electric spark. Cyanogen is stable : not being resolyed into 
its components at a red heat, unless in iron yessels. Much 
less stable howeyer are the several oxides of nitrogen. The 
protoxide, it is true, does not yield up its elements below a 
red heat ; but nitrous acid cannot exist if water be added to 
it ; hypo-nitric acid is decomposed both by water and by 
contact with the various bases ; and nitric acid not only 
readily parts with its oxygen to many metals, but when 
anhydrous, spontaneously decomposes. Here it will 

be well to note, as haying a bearing on what is to follow, how 
characteristic of most nitrogenous compounds is this special 
instability. In all the familiar cases of sudden and violent 
decomposition, the change is due to the presence of nitrogen. 
The explosion of gunpowder results from the readiness with 
which the nitrogen contained in the nitrate of potash, yields 
up the oxygen combined with it. The explosion of gun-cot- 
ton, which also contains nitric acid, is a substantially par- 
allel phenomenon. The various fulminating salts are all 
formed by the union with metals, of a certain nitrogenous 
acid called fiilminic acid ; which is so unstable that it cannot 
be obtained in a separate state. Explosiveness is a property 
of nitro-mannite, and also of nitro-glycerin. Iodide of nitrogen 
detonates on the slightest touch, and often without any assign- 
able cause. Percussion produces detonation in sulphide of 
nitrogen. And the body which explodes with the most 
tremendous violence of any that is known, is the chloride of 
nitrogen. Thus these easy and rapid decompositions, due to 
the chemical indifference of nitrogen, are characteristic. 
When we come hereafter to observe the part which nitrogen 


plays in organio actions, we shall see the significance of this 
extreme readiness shown by its compounds to undergo 
change. Returning from these facts parenthetically 

introduced, we have next to note that though among these 
binary compounds of the four chief organio elements, there 
are a few active ones, yet the majority of them display a 
smaller degree of chemical energy than the average of binary 
compounds. Water is the most neutral of bodies : usually pro- 
ducing little chemical alteration in the substances with which 
it combines ; and being expelled from most of its combinations 
by a moderate heat. Carbonic acid is a relatively feeble acid : 
the carbonates being decomposed by the majority of other acids 
and by ignition. The various hydro-carbons are but narrow 
in the range of their comparatively weak affinities. The 
compounds formed by ammonia have not much stability : they 
are readily destroyed by heat, and by the other alkalies. 
The affinites of cyanogen are tolerably strong ; though they 
yield to Ihose of the chief acids. Of the several oxides of ni- 
trogen it is to be remarked, that while those containing the 
smaller proportions of oxygen are chemically inert, that con- 
taining the'greatest proportion of oxygen (nitric acid) though 
chemically active, in consequence of the readiness with which 
one part of it gives up its oxygen to oxidize a base with 
which the rest combines, is nevertheless driven from all its 
combinations by a red heat. 

These binary compounds, like their elements, are to a con- 
siderable degree characterized by the prevalence among 
them of allotropism ; or, as it is more usually called when 
displayed by compound bodies — isomerism. Professor Graham 
finds reason for thinking that a change in atomic arrange- 
ment of this nature, takes place in water, at or near the 
melting point of ice. The relation between cyanogen and 
paracyanogen is; as we saw, an isomeric one. In the above- 
named series of hydro-carbons, differing from each other only 
in the multiples in which the elements are united, we find 
isomerism becoming what is distinguished as polymerism. 


The like is still more conspicuous in other groups of the 
hydro-carbons, as in the essential oils : sixteen to twenty of 
which are severally isomeric with essential oil of turpentine. 
Here the particular kind of molecular mobility implied by 
these metamorphoses, is well shown : essential oil of turpen- 
tine being converted into a mixture of several of these poly* 
merides, by simple exposure to a heat of 460**. 

There is one further fact respecting these binary compounds 
of the four chief organic elements, which must not be over- 
looked. Those of them which form parts of the living tissues 
of plants and animals (excluding water which has a me- 
chanical function, and carbonic acid which is a product of 
decomposition) are confined to one group — ^the hydro-carbons. 
And of this group, which is on the average characterized by 
comparative instability and inertness, these hydro-carbons 
foimd in living tissues, are among the most unstable and 

§ 3. Passing now to the substances which contain three 
of these chief organic elements, we have first to note that 
along with the greater atomic weight which mostly accom- 
panies their increased complexity, there is, on the average, a 
further marked decrease of molecular mobility. Scarcely any 
of them maintain a gaseous state at ordinary temperatures. 
One class of them only, the alcohols and their derivatives, 
evaporate under the usual atmospheric pressure; but not 
rapidly unless heated. The fixed oils, though they show that 
molecular mobility implied by an habitually liquid state, 
show this in a lower degree than the alcoholic compounds ; 
and they cannot be reduced to the gaseous state without de- 
composition. In their allies, the fats, which are solid unless 
heated, the loss of molecular mobility is still more marked. 
And throughout the whole series of the fatty acids, in which 
to a fixed proportion of oxygen there are successively added 
higher equimultiples of carbon and hydrogen, we see how 
the molecular mobility decreases with the increasing sizes of 


the atoms. In the amylaceons and saccharine group of com* 
pounds, solidity is the habitual state : such of them as can 
assume the liquid form, doing so only when heated to 300^ or 
400° F. ; and decomposing when further heated, rather than 
become gaseous. Resins and gums exhibit general physical 
properties of like character and meaning. 

In chemical stability these ternary compounds, considered 
as a group, are in a marked degree below the binary ones. 
The yarious sugars and kindred bodies, decompose at no yery 
high temperatures. The oils and fats are also readily carbon- 
ized by heat. Besinous and gummy substances are easily 
made to render up some of their constituents. And the 
alcohols with their allies, haye no great power of resisting 
decomposition. These bodies, formed by the union of 

oxygen, hydrogen and carbon, are also, as a class, chemically 
inactiye. The formic and acetic are doubtless energetio 
acids ; but the higher members of the fatty-acid series are 
easily separated from the bases with which they combine. 
Saccharic acid, too, is an acid of considerable power ; and 
sundry of the yegetal acids possess a certain actiyity, 
though an actiyity far less than that of the mineral acids. 
But throughout the rest of the group, there is shown but a 
small tendency to combine with other bodies ; and such com- 
binations as are formed haye usually little permanence. 

The phenomena of isomerism and polymerism are of fre- 
quent occurrence in these ternary compoirnds. Starch and 
dextrine are isomeric. Fruit sugar, starch sugar, eucalyn, 
sorbin, and inosite, are polymeric. Sundry of the yegetal 
acids exhibit similar modifications. And among the resins 
and gums, with their deriyatiyes, molecular re-arrangements 
of this kind are not uncommon. 

One further fact respecting these compounds of carbon, 
oxygen and hydrogen, should be mentioned ; namely, that 
they are diyisible into two classes — ^the one consisting of sub- 
stances that result from the destructiye decomposition of 
organic matter, and the other consisting of substances that 


exist as such in organic matter. These two classes of sub- 
stances exhibit in diflTerent degrees, the properties to which 
we have been directing our attention. The lower alcohols* 
their allies and derivatiyes, which possess greater molecular 
mobility and chemical stability than the rest of these ternary 
compounds, are not found in animal or vegetal bodies. While 
the sugars and amylaceous substances, the fixed oils and fats» 
the gums and resins, which have all of them much less mole- 
cular mobility, and are, chemically considered, more unstable 
and inert, are components of the living tissues of plants and 

§ 4. Among compounds containing all the four chief 
organic elements, a division analogous to that just named 
may be made. There are some which result from the decom* 
position of living tissues; there are others which make 
parts of living tissues in their state of integrity ; and these 
two groups are contrasted in their properties in the same way 
as are the parallel groups of ternary compounds. 

Of the first division, certain products found in the animal 
excretions are the most important, and the only ones that 
need be noted ; such, namely, as urea, kreatine, kreatinine. 
These animal bases exhibit much less molecular mobility than 
the average of the substances treated of in the last section : 
being solid at ordinary temperatures, fusing, where fusible at 
aU, at temperatures aboye that of boiling water, and having 
no power to assume a gaseous state. Chemically considered, 
their stability is low, and their activity but small, in com- 
parison with the stabilities and activities of the simpler com- 

It is, however, the nitrogenous constituents of living tis- 
sues, that display most markedly, those characteristics of which 
we have been tracing the growth. Albumen, fibrin, casein, 
and their allies, are bodies in which that molecular mobility 
exhibited by three of their components in so high a degree, 
is reduced to a minimum. These substances are known only 


in tbe solid state : that is to say, wlien deprived of the water 
usually mixed with them, they do not admit of fusion, much 
less of volatilization. To which add, that they have not even 
that molecular mobility which solution in water implies; 
since, though they form viscid mixtures with water, they do 
not dissolve in the same perfect way as do inorganic com- 
pounds. The chemical characteristics of these sub- 

stances, are instability and inertness carried to the extreme. 
How rapidly albumenoid matters decompose under ordinary 
conditions, is daily seen : the difficulty of every house-wife 
being to prevent them from decomposing. It is true that 
when desiccated and kept from contact with air, they may be 
preserved unchanged for a long period ; but the fact that they 
can only be thus preserved, proves their great instability. It is 
true, also, that these most complex nitrogenous principles are 
not absolutely inert ; since they enter into combinations with 
some bases ; but their unions are very feeble. 

It should be noted, too, of these bodies, that though they 
exhibit in the lowest degree that kind of molecular mobility, 
which implies facile vibration of the atoms as wholes, they ex- 
hibit in a high degree that kind of molecular mobility resulting 
in isomerism, which implies permanent changes in the posi- 
tions of adjacent atoms with respect to each other. Each of 
them has a soluble and insoluble form. In some cases there 
are indications of more than two such forms. And it appears 
that their metamorphoses take place under very slight 
changes of conditions. 

In these most unstable and inert organic compounds, we 
find that the atomic complexity reaches a maximum : not 
only since the four chief organic elements are here united 
with small proportions of sulphur and phosphorus ; but also 
since they are united in high multiples. The peculiarity 
which we found characterized even binary compounds of the 
organic elements, that their atoms are formed not of single 
equivalents of each component, but of two, three, four and 
more equivalents, is carried to the greatest extreme in these 


compounds, that take the leading part in organic actions, 
According to Mulder, the formula of albumen is 10 (G^^ H'^ 
N* 0") + S» P. That is to say, with the sulphur and phos- 
phorus there are united ten equivalents of a compound atom 
containing forty atoms of carbon, thirty-one of hydrogen, 
five of nitrogen, and twelve of oxygen : the atom being thus 
made up of nearly nine hundred ultimate atoms. 

§ 6. Did space permit, it would be useful, here to consider 
in detail, the interpretations that may be given of the pecu- 
liarities we have been tracing : bringing to their solution, 
those general mechanical principles which are now found to 
hold true of molecules as of masses. But it must suffice 
briefly to indicate the conclusions that such an inquiry pro- 
mises to bring out. 

Proceeding on mechanical principles, it may be argued that 
the molecular mobility of a substance must depend partly on 
the inertia of its molecules ^ partly on the intensity of their 
mutual polarities ; partly on their mutual pressure, as deter- 
mined by the density of their aggregation, and (where the 
molecules are compound) partly*on the molecular mobilities 
of their component molecules. Whence it is to be inferred 
that any three of these remaining constant, the molecular 
mobility will vary as the fourth. Other things equal, there- 
fore, the molecular mobility of atoms must decrease as their 
masses increase ; and so there must result that general pro* 
gression we have traced, from the high molecular mobility 
of the uncombined organic elements, to the low molecular 
mobility of those large-atomed substances into which they are 
ultimately compounded. 

Applying to atoms the mechanical law which holds of 
masses, that since inertia and gravity increase as the cubes 
of the dimensions while cohesion increases as their squares, 
the self-sustaining power of a body becomes relatively 
smaller as its bulk becomes greater ; it might be argued that 
these large, aggregate atoms which constitute organic sub- 


stance, are mechanically weak — are lees able than simpler 
atoms to bear, without alteration, the forces falling on them. 
That very massiveness which renders them less mobile, enables 
the physical forces acting on them more readily to change the 
relative positions of their component atoms ; and so to pro- 
duce what we know as re-arrangements and decompositions. 
Further, it seems a not improbable conclusion, that this 
formation of large aggregates of elementary atoms, and re- 
sulting diminution of self-sustaining power, must be accom- 
panied by a decrease of those contrasts of dimension to 
which polarity is ascribable. A sphere is the figure of equi- 
librium which any aggregate of units tends to assume, under 
the influence of simple mutual attraction. Where the num- 
ber of units is small and their mutual polarities are decided, 
this proclivity towards spherical grouping will be overcome 
by the tendency towards some more special form, determined 
by their mutual polarities. But it is manifest that in pro- 
portion as an aggregate atom becomes larger, the effects of 
simple mutual attraction must become relatively greater; 
and so must tend to mask the effects of polar attraction. 
There will consequently be apt to result in highly com- 
pound atoms like these organic ones containing nine hun- 
dred elementary atoms, such approximation to the spherical 
form as must involve a less distinct polarity than in simpler 
atoms. If this inference be correct, it supplies us with an ex- 
planation both of the chemical inertness of these most com- 
plex organic substances, and of their inability to crystallize. 

§ 6. Here we are naturally introduced to another aspect of 
our subject — an aspect of great interest. Professor Graham 
has recently published a series of important researches, which 
promise to throw much light on the constitution and changes 
of organic matter. He shows that solid substances exist un- 
der two forms of aggregation — the colloid or jelly-like, and the 
crystalloid or crystal- like. Examples of the last are too fa- 
miliar to need specifying. Of the first may be named such 


instances as ^'hydrated silicic acid^ hydrated alumina, and 
other metallic peroxides of the aluminous class, when they exist 
in the soluble form ; with starch, dextrine and the gums, cara- 
mel, tannin, albumen, gelatine, vegetable and animal extractive 
matters/' Describing the properties of colloids, Professor 
Graham says : — '' Although often largely soluble in water, 
they are held in solution by a most feeble force. They ap- 
pear singularly inert in the capacity of acids and bases, and 
in all the ordinary chemical relations." • ♦ ♦ "Al- 
though chemically inert in the ordinary sense, colloids 
possess a compensating activity of their own arising out of 
their physical properties. While the rigidity of the crystal- 
line structure shuts out external impressions, the softness of 
the gelatinous colloid partakes of fluidity, and enables the 
colloid to become a medium of liquid diffusion, like water 
itself." ♦ ♦ ♦ <« Hence a wide sensibility on the part of 
colloids to external agents. Another and eminently charac- 
teristic quality of colloids is their mutability." * ♦ ♦ « The 
solution of hydrated silicic acid, for instance, is easily obtain- 
ed in a state of purity, but it cannot be preserved. It may 
remain fluid for days or weeks in a sealed tube, but is sure to 
gelatinize and become insoluble at last. Nor does the change 
of this colloid appear to stop at that point ; for the mineral 
forms of silicic acid, deposited from water, such as flint, are 
often found to have passed, during the geological ages of 
their existence, from the vitreous or colloidal into the crystal- 
line condition (H. Rose). The colloid is, in fact, a dynami- 
cal state of matter, the crystalloidal being the statical 
condition. The colloid possesses energia. It may be looked 
upon as the primary source of the force appearing in the 
phenomena of vitality. To the gradual manner in which 
colloidal changes take place (for they always demand time as 
an element) may the characteristic protraction of chemico- 
organic changes also be referred." 

The class of colloids includes not only all those most com- 
plex nitrogeneous compounds characteristic of organic tissue, 


and sundry of the oxy-hydro-oarbons found along with them ; 
but, significantly enough, it includes several of those sub- 
stances classed as inorganic, which enter into organized 
structures. Thus silica, which is a component of many 
plants, and constitutes the spicules of sponges as well as the 
shells of many foraminifera and infusoria, has a colloid, as 
well as a crystalloid, condition. A solution of hydrated silicic 
acid, passes in the course of a few days into a solid jelly that 
is no longer soluble in water ; and it may be suddenly thus 
coagulated by a minute portion of an alkaline carbonate, as 
well as by gelatine, alumina, and peroxide of iron. This last- 
named substance^ too — peroxide of iron — which is an ingre* 
dient in the blood of mammals and composes the shells of 
certain protozoa, has a colloid condition. " Water containing 
about one per cent, of hydrated peroxide of iron in solution, 
has the dark red colour of venous blood." ♦ ♦ ♦ « The 
red solution is coagulated in the cold by traces of sulphuric 
acid, alkalies, alkaline carbonates, sulphates, and neutral salts 
in general." ♦ ♦ ♦ «< The coagulum is a deep red-coloured 
jelly, resembling the clot of blood but more transparent. 
Indeed, the coagulum of this colloid is highly suggestive 
of that of blood, from the feeble agencies which suffice to 
effect the change in question, as well as from the appearance 
of the product." The jelly thus formed soon becomes, like 
the lajst, insoluble in water. Lime also, which is so important 
a mineral element in living bodies, animal and vegetal, 
enters into a compound belonging to this class. "The 
well-known solution of lime in sugar, forms a solid coagulum 
when heated. It is probably, at a high temperature, entirely 

Generalizing some of the facts which he gives, Professor 
Graham says — ''The equivalent of a colloid appears to be 
always high, although the ratio between the elements of the 
substance may be simple. Gummic acid, for instance, may 
be represented by C" H" 0" ; but, judging from the small 
proportions' of lime and potash which suffice to neutralize this 



acid, the true Dumbers of its formula must be several times 
greater. It is difficult to avoid associating the inertness of 
colloids with their high equivalents, particularly where the 
high number appears to be attained by the repetition of a 
small number. The inquiry suggests itself whether the col- 
loid molecule may not be constituted by the grouping 
together of a number of smaller crystalloid molecules, and 
whether the basis of colloidality may not really be this com- 
posite character of the molecule." 

§ 7. A further contrast between colloids and crystalloids, 
is equally significant in its relations to vital phenomena. 
Professor Graham points out that the marked differences in 
volatility displayed by different bodies, are paralleled by 
differences in the rates of diffusion of different bodies through 
liquids. As alcohol and ether at ordinary temperatures, and 
various other substances at higher temperatures, diffuse them- 
selves in a gaseous form through the air ; so, a substance in 
aqueous solution, when placed in contact with a mass of 
water (in such way as to avoid mixture by circulating currents) 
diffiises itself through this mass of water. And just as there 
are various degrees of rapidity in evaporation, so there are 
various degrees of rapidity in diffusion : " the range also in 
the degree of diffusive mobility exhibited by different sub- 
stances appears to be as wide as the scale of vapour-tensions." 
This parallelism is what might have been looked for ; since 
the tendency to assume a gaseous state, and the tendency to 
spread in solution through a liquid, are both consequences of 
molecular mobility. It also turns out, as was to be expected, 
that diffusibility, like volatility, has, other things equal, a re- 
lation to atomic weight — (other things equal, we must say, 
because molecular mobility must, as pointed out in § 5, be 
affected by other properties of atoms, besides their inertia). 
Thus the substance most rapidly diffused of any on which 
Professor Graham experimented, was hydro-chloric acid — a 
compound which is of low atomic weight, is gaseous save 


under a pressure of forty atmospheres^ and ordinaiily exists 
as a Kquid, only in combination with water. Again, " hydrate 
of potash may be said to possess double the velocity of divi- 
sion of sulphate of potash, and sulphate of potash again double 
the velocity of sugar, alcohol, and sulphate of magnesia," — 
differences which have a general correspondence with differ- 
ences in the massiveness of the atoms. 

But the fact of chief interest to us here, is that the rela- 
tively small-atomed crystalloids have immensely greater 
diffusive power than the relatively large-atomed colloids. 
Among the crystalloids themselves, there are marked differ- 
,ences of diffusibility ; and among the colloids themselves, 
there are parallel differences, though less marked ones. But 
these differences are small compared with that between the 
diffusibility of the crystalloids as a class, and the diffusibility 
of the colloids as a class. Hydro-chloric acid is seven times 
as diffusible as sulphate of magnesia ; but it is fifty times as 
diffusible as albumen, and a hundred times as diffusible as 

These differences of diffusibility manifest themselves with 
nearly equal distinctness, when a permeable septum is placed 
between the solution and the water. And the result is, that 
when a solution contains substances of different diffiisibilities, 
the process of dialysis, as Professor Graham calls it, becomes 
a means of separating the mixed substances : especially when 
such mixed substances are partly crystalloids and partly col- 
loids. The bearing of this fact on organic processes will be 
obvious. Still more obvious will its bearing be, on 

joining it with the remarkable fact, that while crystalloids 
can diffuse themselves through colloids nearly as rapidly as 
through water, colloids can scarcely difiuse themselves at all 
through other colloids. From a mass of jelly containing 
salt, into an adjoining mass of jelly containing no salt, the 
salt spread more in eight days than it spread through water 
in seven days ; while the spread of " caramel through the 

jelly appeared scarcely to have begun after eight davs had 

2 ♦ 


elapsed.** So that we must regard the colloidal compounds 
of which organisms are built, as having by their physical 
nature, the ability to separate colloids from crystalloids, and 
to let the crystalloids pass through them with scarcely any 

One other result of these researches on the relative diflEii- 
sibilities of different substances, has a meaning for us. Pro- 
fessor Graham finds, that not only does there take place by 
dialysis, a separation of mixed substances which are unlike in 
their molecidar mobilities ; but also that combined substances 
between which the affinity is feeble, will separate on the 
dialyzer, if their molecular mobilities are strongly con- 
trasted. Speaking of the hydro-chlorate of peroxide of 
iron, he says, " such a compound possesses an element of 
instability in the extremely unequal diffusibility of its 
constituents ; *' and he points out that when dialyzed, the 
hydro-chloric acid gradually diffuses away, leaving the 
colloidal peroxide of iron behind. Similarly, he remarks of 
the peracetate of iron, that it " may be made a source of 
soluble peroxide, as the salt referred to is itself decomposed 
to a great extent by diffusion on the dialyzer." Now this 
tendency to separate displayed by substances that differ 
widely in their molecular mobilities, though usually so 
far antagonized by their aff nities as not to produce sponta-» 
neous decomposition, must, in all cases, induce a certain 
readiness to change which would not else exist. The un- 
equal mobilities of the combined atoms, must give disturbing 
forces a greater power to work transformations than they 
would otherwise have. Hence the probable significance of a 
fact named at the outset, that while three of the chief organic 
elements have the greatest atomic mobilities of any elements 
known, the fourth, carbon, has the least atomic mobility of 
known elements. Though, in its simple compounds, the 
affinities of carbon for the rest are strong enough to prevent 
the effects of this great difference from clearly showing them- 
selves ; yet there seems reason to think^ that in those com- 


plex compoands composing organic bodics^-compoiinds in 
which there are various cross affinities leading to a state 
of chemical tension — ^this extreme difference in the molecular 
mobilities must be an important aid to molecular re-arrange* 
ments. In short, we are here led by concrete evidence to the 
conclusion which we before drew from first principles, that 
this great unlikeness among the combined units must facili- 
tate differentiations. 

§ 8. A portion of organic matter in a state to exhibit 
those phenomena which the biologist deals with, is, however, 
something far more complex than the separate organic mat- 
ters we have been studying ; since a portion of organic 
matter in its integrity, contains several of these. 

In the first place, no one of those coUoids which make up 
the mass of a living body^ appears capable of carrying on 
vital changes by itself: it is always associated with other 
colloids. A portion of animal-tissue, however minute, almost 
always contains more than one form of protein-substance : 
differ^t chemical modifications of albumen and gelatine are 
present together, as well as, probably, a soluble and insoluble 
modification of each ; and there is usually more or less of 
fatty matter* In a single vegetal cell, the niinute quantity 
of nitrogenous colloid present, is imbedded in colloids of the 
non-nitrogenous class. The microscope makes it at once 
manifest, that even the smallest and simplest organic forms 
are not absolutely homogeneous. 

Further, we have to3 contemplate organic tissue, formed 
of mingled colloids in both soluble and insoluble states, as 
permeated throughout by crystalloids. Some of these crys- 
talloids, as oxygen,* water, and perhaps certain salts, are 
agents of decomposition ; some, as the saccharine and fatty 

* It will perhaps seem straDge to daas oxygen as a crystalloid. Bat inasmuch 
as the crystalloids are distinguished from the colloids hy their atomic simplicity, 
and inasmuch as sundry gases are reducible to a crystalline state, we are justified 
in so classing it. 


matters, are probably materials for decomposition ; and some, 
as carbonic acid, water, nrea, kreatine, and kreatinine, are 
products of decomposition. Into the mass of mingled colloids, 
mostly insoluble and where soluble of very low molecular 
mobility or diffusive power, we have constantly passing, crys- 
talloids of high molecular mobility or diffusive power, that 
are capable of decomposing these complex colloids ; and from 
these complex colloids, so decomposed, .there result other 
crystalloids (the two chief ones extremely simple and mobile, 
and the rest comparatively so) which di£Euse away as rapidly 
as they are formed. 

And now we may clearly see the necessity for that pecu- 
liar composition which we find in organic matter. On the 
one hand, were it not for the extreme molecular mobility 
possessed by three of its chief elements out of the four ; and 
were it not for the consequently high molecular mobility of 
their simpler compounds ; there could not be this quick escape 
of the waste products of organic action ; and there could not 
be that continuously active change of matter which vitality 
implies. On the other hand, were it not for the union of 
these extremely mobile elements into immensely complex 
compounds, having relatively vast atoms that are made com* 
paratively immobile by their inertia, there could not result 
that mechanical fixity which prevents the components of liv- 
ing tissue from diffiising away along with the effete matters 
produced by the decomposition of tissue. 

§ 9. Thus in the substances of which organisms are 
composed, the conditions necessary to that re-distribution of 
Matter and Motion which constitutes Evolution, are fulfilled 
in a far higher degree than at first appears. 

The mutual affinities of the chief organic elements are 
not active within the limits of those temperatures at which 
organic actions take place ; and one of these elements is 
especially characterized by its chemical indifference. The 
compounds formed by these elements in ascending grades of 


complexity, become progressively less stable. And those 
most complex compounds into which all these four elements 
enter, together with small proportions of two other elements 
that very readily oxidize, have an instability so great that 
decomposition ensues under ordinary atmospheric conditions. 

Among these elements out of which living bodies are built, 
there is an unusual tendency to unite in multiples ; and so to 
form groups of products which have the same chemical com- 
ponents, but, being diflferent in their modes of aggregation, 
possess different properties. This prevalence among them of 
isomerism and polymerism, shows, in another way, the special 
fitness of organic substances for undergoing re-distributions. 

In those most complex compounds that are instrumental 
to vital actions, there exists a kind and degree of molecular 
mobility which constitutes the plastic quality fitting them for 
organization. Instead of the extreme molecular mobility 
possessed by three out of the four organic elements in their 
separate states — ^instead of the diminished, but still great, 
molecular mobility possessed by their simpler combinations, 
the gaseous cf^d liquid characters of which unfit them for 
showing to. any extent the process of Evolution — instead of 
the properties of their less simple combinations, which, 
when not made imduly mobile by heat, assume the unduly 
rigid form of crystals ; we have in these colloids, of which 
organisms are mainly composed, just the required com- 
promise between fluidity and solidity. They cannot be re- 
duced to the imduly mobile conditions of liquid and gas ; and 
yet they do not assume the unduly fixed condition usually cha- 
racterizing solids. The absence of power to unite together in 
polar arrangement, leaves their atoms with a certain freedom 
of relative movement which makes them sensitive to small 
forces, and produces plasticity in the aggregates composed 
of them. 

While the relatively great inertia of these large and com- 
plex organic atoms, renders them comparatively incapable 
of being set in motion by the ethereal imdulations, and so re- 


duced to less coherent forms of aggregation ; there is reason 
to think that this same inertia facilitates changes of arrange- 
ment among their constituent atoms ; since, in proportion as 
an incident force impresses but little motion on a mass, it is 
the better able to impress motion on the parts of the mass in 
relation to each other. And it is further probable that the 
extreme contrasts in molecular mobilities among the compo- 
nents of these highly complex atoms, aid in producing modi- 
fiabilitj of arrangement among them. 

Lastly, the great difference in diffiisibility between colloids 
and crystalloids, makes possible in the tissues of organisms, 
a specially rapid re-distribution of matter and motion ; both 
because colloids, being easily permeable by crystalloids, can 
be chemically acted on throughout their whole mass, in- 
stead of only on their surfaces ; and because the products of 
decomposition, being also crystalloids, can escape as fast as 
they are produced, leaving room for further like transforma- 
tions. So that while the composite atoms of which organic 
tissues are built up, possess that low molecular mobility fit- 
ting them for plastic purposes, it results from the extreme 
molecular mobilities of their ultimate constituents, that the 
waste products of vital activity escape as fast as they are 

To all which add, that the state of warmth, or increased 
molecular vibration, in which all the higher organisms are 
kept, increases these various facilities for re-distribution : not 
only as aiding chemical changes, but as accelerating the dif- 
fusion of crystalloid substances. 



§ 10. To some extent, the parts of every body are changed 
in their arrangement by any incident mechanical force. 
But in organic bodies, the changes of arrangement produced 
by mechanical forces are usually conspicuous. It is a dis- 
tinctive mark of colloids, that they yield with great readiness 
to pressures and tensions ; and that they yet recover, more 
or less completely, their original shapes, when the pres- 
sures or tensions cease. It is clear that without this 
pliability and el^ticity, most organic actions would be im- 
possible. Not only temporary but permanent alter- 
ations of form are facilitated by this colloid character of 
organic matter. Continued pressure on living tissue, by 
modifying the processes going on in it, (perhaps retarding 
the absorption of new material to replace the old that has 
decomposed and diffused away,) gradually diminishes and 
finally destroys its power of resuming the outline it had at 
first. Thus the matter of which organisms are built up, is 
modifiable by arrested momentum or by continuous strain, 
in a far greater degree than is ordinary matter. 

§ 11. Sensitiveness to certain forces that are quasi- 
mechanical, if not mechanical in the usual sense, is seen in 
two closely-related peculiarities displayed by organic matter 


as well as other matter that assumes the same state of mole- 
cular aggregation. 

Colloids take up by a power that has been called " capillary 
affinity/' a large quantity of water : unJergoing at the same 
time great increase of bulk with change of form. Conversely, 
with like readiness, they give up this water by evaporation : 
resimiing more or less completely their original states. 
Whether resulting from capillarity, or from the relatively 
great diffusibility of water, or from both; these changes 
are to be here noted as showing another mode in which 
the arrangement of parts in organic bodies, is affected by 
mechanical forces. 

In what is called osmose, we have a fiirther mode of allied 
kind. When on opposite sides of a permeable septum, and 
especially a septum of colloidal substance, are placed miscible 
solutions of different densities, a double transfer takes place : 
a large quantity of the less dense solution finds its way through 
the septum into the more dense solution ; and a small quan- 
tity of the more dense finds its way into the less dense — one 
result being a considerable increase in the bulk of the more 
dense at the expense of the less dense. This process, which 
appears to depend on several conditions, is not yet fully un- 
derstood. But be the explanation what it may, the process 
is one that tends continually to work alterations in organic 
bodies. Through the surfaces of plants and animals, transfers 
of this kind are ever taking place. Very many of the con- 
spicuous changes of form undergone by organic germs, are 
due mainly to the permeation of their limiting membranes 
by the surrounding liquids. 

It should be added that besides the direct alterations which 
the imbibition and transmission of water and watery solutions 
by colloids produce in organic matter, they produce indirect 
alterations. Being instrumental in conveying into the tissues 
the agents of chemical change, and conveying out of them 
the products of chemical change, they aid in carr3'ing on 
other re- distributions. 


§ 12. As elsewhere shown {First Principka, § 103) Heat, or 
a raised state of molecular vibration, enables incident forces 
more easily to produce changes of molecular arrangement in 
organic matter. But besides this, it conduces to certain vital 
changes in so direct a way as to become their chief cause. 

The power of the organic colloids to imbibe water, and to 
bring along with it into their substance the materials which 
work transformations, would not be continuously operative 
if the water imbibed were to remain. It is because it escapes, 
and is replaced by more containing more materials, that the 
succession of changes is maintained. Among the higher 
animals and higher plants its escape is facilitated by evapor- 
ation. And the rate of evaporation is, other things equal, 
determined by heat. Though the current of sap in 

a tree is mainly caused by some action, probably osmotic, 
that is at work in the roots; yet the loss of water from 
the surfaces of the leaves, and the consequent absorption 
of more sap into the leaves by capillary attraction, must 
largely aid the circulation. The drooping of a plant when 
exposed to the sunshine while the earth round its roots is 
dry, shows us how evaporation empties the sap- vessels ; and 
the quickness with which a withered slip revives on being 
placed in water, shows us the part which capillary action 
plays. In so far then, as the evaporation from a plant's sur- 
face helps to produce currents of sap through the plant, 
we must regard the heat which produces this evaporation 
as a part-cause of those re-distributions of matter which 
these currents effect. In terrestrial animals, heat 

similarly aids the changes that are going on. The exha- 
lation of vapour from the lungs and the surface of the skin, 
forming the chief escape of the water that is swallowed, 
conduces to the maintenance of those currents through the 
tissues, without which the functions would cease. For 
though the vascular system distributes nutritive fluids in 
ramified channels through the body ; yet the absorption of 
these fluids into tissues, partly depends on the escape of fluids 


which the tissues already contain. Hence, to tlie extent that 
such escape is facilitated by evaporation, and this evaporation 
facilitated by heat, heat becomes an agent of re-distribution 
in the animal organism. 

§13. Light, which is now known to modify many inor- 
ganic compounds — which works those chemical changes 
utilized in photography, causes the combinations of certain 
gases, alters the molecular arrangements of many crystals, 
and leaves traces of its action even on substances that are ex- 
tremely stable, — may be expected to produce marked effects 
on substances so complex and unstable as those which make 
up organic bodies. It does produce such marked effects ; 
and some of them are among the most important that 
organic matter undergoes. 

The molecular changes wrought by light in animals, are 
but of secondary moment. There is the darkening of the 
skin that follows exposure to the sim's rays. There are 
those alterations in the retina which cause in us sensations 
of colours. And on certain eyeless creatures that are semi* 
transparent, the light permeating their substance works 
some effect evinced by movement. But speaking generally, 
the opacity of animals limits the action of light to their 
surfaces; and so renders its direct physiological influence 
but small.* On plants, however, the solar rays that 

produce in us the impression of yellow, are the immediate 
agents of those molecular changes through which are hourly 
accumulated the materials for further growth. Experiments 
have shown that when the sun shines on living leaves, they 
begin to exhale oxygen and to accumulate carbon and 
hydrogen — results which are traced to the decomposition by 
the solar rays, of the carbonic acid and water absorbed. 
It is now an accepted conclusion that, by the help of certain 

* The increase of respiration found to result from the presence of light, i^ 
probably an indirect effect. It is most likely due to the reception of more vivid 
impressions through the eyes, and to the consequent nervous stimulation. 


classes of the ethereal undulations penetrating their leaves, 
plants are enabled to separate from the associated oxygen, 
those two elements of which their tissues are chiefly built 

This transformation of ethereal undulations into certain 
molecular re-arrangements of an unstable kind, on the over- 
throw of which the stored-up forces are liberated in new 
forms, is a process that underlies all organic phenomena. It 
will therefore be well, if we pause a moment to consider whe- 
ther any proximate interpretation of it is possible. Certain 
Tecent researches in molecular physics, give us some clue to 
its nature. 

The elements of the problem are these : — The atoms of 
several ponderable matters exist in combination : those that 
are combined having strong affinities, but having also affin- 
ities less strong for some of the surrounding atoms that are 
otherwise combined* The atoms thus united, and thus mixed 
among others with which they are capable of uniting, are 
exposed to the undulations of a medium that is relatively so 
rare as to seem imponderable. These undulations are of 
numerous kinds : they differ greatly in their lengths, or in 
the frequency with which they recur at any given point. 
And under the influence of undulations of a certain frequency, 
some of these atoms are transferred from atoms for which they 
have a stronger affinity, to atoms for which they have a weaker 
affinity. That is to say, particular orders of waves of a rela- 
tively imponderable matter, remove particular atoms of pon- 
derable matter from their attachments, and carry them within 
reach of other attachments. Now the discoveries of 

Bunsen and Kirchoff respecting the absorption of particular 
luminiferous undulations by the vapours of particular sub- 
stances, joined with Prof. Tyndall's discoveries respecting 
the absorption of heat by gases, show very clearly that the 
atoms of each substance have a rate of vibration in harmony 
with ethereal waves of a certain length, or rapidity of recur- 
rence. Every special kind of atom can be made to oscillate 


by a special order of ethereal waves, which are absorbed in 
producing its oscillations ; and can by its oscillations generate 
this same order of ethereal waves. Whence it appears that 
immense as is the difference in density between ether and 
ponderable matter, the waves of the one can set the atoms of 
the other in motion, when the successive impacts of the waves 
are so timed as to correspond with the oscillations of the 
atonuk The effects of the waves are, in such case, cumula- 
tive ; and each atom gradually acquires a momentum made up 
of countless infinitesimal momenta. Note further, 

that imless the members of a chemically-compound atom are 
so bound up as to be incapable of any relative movements (a 
supposition at variance with the conceptions of modem science) 
we must conceive them as severally able to vibrate in unison 
or harmony with those same classes of ethereal waves that 
affect them in their uncombined states. While the compound 
atom as a whole, will have some new rate of oscillation de- 
termined by its attributes as a whole ; its components will 
retain their original rates of oscillation, subject only to modifi* 
cations by mutual influence. Such being the cir- 

cumstances of the case, we may partially understand how 
the sun's rays can effect chemical decompositions. If the 
members of a binary atom stand so related to the undulations 
falling on them, that one is thrown into a state of increased 
oscillation and the other not; it is manifest that there 
must arise a tendency towards the dislocation of the two — a 
tendency which may or may not take effect, according to the 
weakness or strength of their imion, and according to the 
presence or absence of collateral affinities. This inference is 
in harmony with several significant facts. Dr Draper 
remarks that " among metallic substances (compounds) those 
first detected to be changed by light, such as silver, gold, 
mercury, lead, have all high atomic weights ; and such as 
sodium and potassium, the atomic weights of which are low, 
appeared to be less changeable." As here interpreted, the 
fact specified amounts to this; that the compounds most 


readily decomposed by lights are those in which there 
is a marked contrast between the atomic weights of the 
constituents^ and probably therefore a marked contrast 
between the rapidities of their vibrations. The circumstance, 
too, that different chemical compounds are decomposed or 
modified in different parts of the spectrum, implies that there 
is a relation between special orders of undulations and special 
orders of composite atoms — doubtless a correspondence 
between the rates of these undulations and the rates of 
oscillation which some of the components of such atoms 
will assume. Strong confirmation of this view may 

be drawn from the decomposing actions of those longer 
ethereal waves which we perceive as heat. ^ On contemplating 
the whole series of binary compounds, we see that the ele- 
ments which are most remote in their atomic weights, as 
hydrogen and the noble metals, will not combine at all : their 
vibrations are so unlike that they cannot keep together 
under any conditions of temperature. If again we look at a 
smaller group, as the metallic oxides, we see that whereas 
those metals that have atoms nearest in weight to the atoms 
of oxygen, cannot be separated from oxygen by heat, even 
when it is joined by a powerful collateral afiinity; those 
metals which differ more widely from oxygen in their atomic 
weights, can be de-oxidized by carbon at high temperatures ; 
and those which differ from it most widely, combine with it 
very reluctantly, and yield it up if exposed to thermal undu-. 
lations of moderate intensity. And here indeed, remem-^ 
bering the relations among the atomic weights in the two 
cases, may we not suspect a close analogy between the de- 
oxidation of a metallic oxide by carbon under the influence 
of the longer ethereal waves, and the de-carbonization of 
carbonic acid by hydrogen under the influence of the shorter 
ethereal waves P 

These conceptions help us to some dim notion of the mode 
in which changes are wrought by light in the leaves of plants. 
Among the several elements concerned, there are wide differ- 


ences in molecular mobility, and probably in the rates of 
molecular vibration. Each is combined with one of the others ; 
but is capable of forming various combinations with the rest. 
And they are severally in presence of a complex compound 
into which they all enter, and which is ready to assimilate 
with itself the new compoimd atoms that they form. Certain 
of the ethereal waves Mling on them when thus arranged, 
there results a detachment of some of the combined atoms 
and a union of the rest. And the conclusion suggested is, 
that the induced vibrations among the various atoms as at 
first arranged, are so incongruous as to produce instability ; 
and to give collateral affinities the power to work a re- 
arrangement, whiib, though less stable under other conditions, 
is more stable in the presence of these particular undula- 
tions. There seems, indeed, no choice but to conceive 
the matter thus. An atom united with one for which it has 
a strong affinity, has to be transferred to another for which 
it has a weaker affinity. This transfer implies motion. The 
motion is given by the waves of a medium that is relatively 
imponderable. No one wave of this imponderable medium 
can give the requisite motion to this atom of ponderable 
matter : especially as the atom is held by a positive force besides 
its inertia. The motion required can hence be given only 
by successive waves ; and that these may not destroy each 
other's effects, it is needful that each shall strike the atom 
just when it has completed that recoil produced by the impact 
of previous ones. That is, the ethereal undulations must 
coincide in rate with the oscillations of the atom, determined 
by its inertia and the forces acting on it. It is also requisite 
that the rate of oscillation of the atom to be detached, shall 
differ from that of the atom with which it is united ; since 
if the two oscillated in unison, the ethereal waves would not 
tend to separate them. And, finally, the successive impactsf 
of the ethereal waves must be accumulated, until the resulting 
oscillations have become so wide in their sweep as greatly to 
weaken the cohesion of the united atoms, at the same time 


that they bring one of them within reach of other atoms with 
which it will combine. In this way only does it seem possible 
for such a force to produce such a transfer. More- 

over, while we are thus enabled to conceive how light may 
work these molecular changes ; we also gain an insight into 
the method by which the insensible motions propagated to 
us from the sun, are treasured up in such way as afterwards 
to generate sensible motions. By the accumulation of in- 
finitesimal impacts, atoms of ponderable matter are made to 
oscillate. The quantity of motion which each of them 
eventually acquires, effects its transfer to a position of un- 
stable equilibrium, from which it can afterwards be readily 
dislodged. And when so dislodged, along with other atoms 
similarly and simultaneously affected, there is suddenly given 
out all the motion which had been before impressed on it. 

Speculation aside, however, that which it concerns us to 
notice, is the broad fact that light is an all-important agent 
of molecular changes in organic substances. It is not here 
necessary for ns to ascertain how light produces these compo- 
sitions and decompositions : it is necessary only for us to 
observe that it does produce them. That the characteristic 
matter called chlorophyll, which gives the green colour to 
leaves, makes its appearance \shenever the blanched shoots of 
plants are exposed to the sun ; that the petals of flowers, 
imcoloured while in the bud, acquire their bright tints as 
they unfold; and that on the outer surfaces of animals, 
analogous changes are induced ; are wide inductions which 
are enough for our present purpose. 

§ 14. "We come next to the agency of chief importance 
among those that work changes in organic mutter ; namely, 
chemical affinity. How readily vegetal and animal substances 
are modified by other substances put in contact with them, 
we see daily illustrated. Besides the many compounds which 
cause the death of an organism into which they are put, we 
have the much greater number of compounds which w^ork 


those milder effects termed medicinal — effects implying, like 
the others, molecular re-arrangements. Indeed, nearly all 
soluble chemical compounds, natural and artificial, produce^ 
when taken into the body, alterations that are more or less 
conspicuous in their results. 

After what was shown in the last chapter, it will be mani- 
fest that this extreme modifiability of organic matter by 
chemical agencies, is the chief cause of that active molecular 
re-arrangement which organisms, and especially animal or- 
ganisms, display. In the two fundamental functions of 
nutrition and respiration, we have the means by which the 
supply of materials for this active molecular re-arrangement 
is maintained. 

Thus the process of animal nutrition consists in the absorp- 
tion, partly of those complex substances that are thus highly 
capable of being chemically altered, and partly in the absorp- 
tion of simpler substances capable of chemically altering 
them. The tissues always contain small quantities of alka- 
line and earthy salts, which enter the system in one form 
and are excreted in another. Though we do not know spe- 
cifically the parts which these salts play, yet from their 
universal presence, and from the transformations which they 
undergo in the body, it may be safely inferred that their 
chemical affinities are instrumental in working some of the 
metamorphoses ever going on. 

The inorganic substance, however, on which mainly depend 
these metamorphoses in organic matter, is not swallowed 
along with the solid and liquid food, but is absorbed from 
the surrounding medium — air or water, as the case may be. 
Whether the oxygen taken in, either, as by the lowest 
animals, through the general surface, or, as by the higher 
animals, through respiratory organs, is the immediate cause 
of those molecular changes that are ever going on through- 
out the living tissues ; or whether the oxygen, playing the 
part of scavenger, merely aids these changes by carrying 
away the products of decompositions otherwise caused; it 


equally remains true, tliat these changes are maintained by 
its instrumentalityt Whether the oxygen absorbed and 
diffused through the system^ effects a direct oxidation of the 
organic colloids which it permeates ; or whether it first leads 
to the formation of simpler and more oxidized compounds, 
that are afterwards further oxidized and reduced to still 
simpler forms ; matters not, in so far as the general result is 
concerned. In any case it holds good, that the substances 
of which the animal body is built up, enter it in a but 
slightly oxidized and highly imstable state ; while the great 
mass of them leave it in a fully oxidized and stable state. 
It follows, therefore, that whatever the special changes gone 
through, the general process is a falling from a state of un- 
stable chemical equilibrium, to a state of stable chemical 
equilibrium. Whether this process be direct or indirect, 
the total molecular re-arrangement and the total motion 
given out in effecting it, must be the same. 

§ 15. There is another species of re-distribution among 
the component imits of organisms, which is not immediately 
effected by the affinities of the units concerned, but is me- 
diately effected by other affinities ; and there is reason to 
think that the re-distribution thus caused, is important in 
amount, if not indeed the most important. In ordinary cases 
of chemical action, the two or more substances concerned^ 
themselves undergo changes of molecular arrangement ; and 
the changes are confined to the substances themselves. But 
there are other cases in which the chemical action going on, 
does not end with the substances at first concerned ; but sets 
going chemical actions, or changes of molecular arrangement, 
among surroimding substances that would else remain qui- 
escent. And there are yet further cases in which mere 
contact with a substance that is itself quiescent, will cause 
other substances to undergo rapid metamorphoses. In 

what we call fermentation, the first species of this communi- 
cated chemical action is exemplified. One part of yeast, 

3 • 


while itself undergoing molecular changes, will convert 100 
parts of sugar into alcohol and carbonic acid ; and during its 
own decomposition, one part of diastase " is able to effect the 
transformation of more than 1000 times its weight of starch 
into sugar." As illustrations of the second species 

may be mentioned those changes which are suddenly produced 
in many colloids by minute portions of various substances 
added to them — substances that are not undergoing any 
manifest transformation, and suffer no appreciable effect 
from the contact. The nature of the first of these two 

kinds of communicated molecular change, which here chiefly 
concerns us, may be rudely represented by certain visible 
changes that are communicated from mass to mass, when a 
series of masses has been arranged in a special way. The 
simplest example is that furnished by the child's play of 
setting bricks on end in a row, in such positions that when 
the first is overthrown it overthrows the second ; the second^ 
the third ; the third, the fourth ; and so on to the end of the 
row. Here we have a number of units severally placed, in 
unstable equilibrium, and in such relative positions that each, 
while falling into a state of stable equilibrium, gives an im- 
pulse to the next, sufficient to make the next, also, fall from 
unstable to stable equilibrium. Now since among mingled 
compound atoms, no one can undergo change in the arrange- 
ment of its parts without a molecular motion that must cause 
some disturbance all around ; and since an adjacent atom 
disturbed by this communicated motion, may have the arrange- 
ment of its constituent molecules altered, if it is not a stable 
arrangement ; and since we know, both that the atoms which 
are changed by this so-called catalysis are unstable, and that 
the atoms resulting from their change are mm'e stable ; it 
seems probable that the transformation is really analogous, 
in principle, to the familiar one named. Whether thus 
interpretable or not, however, there is great reason for think- 
ing that to this kind of action, is due a large amount of vital 


metamorphosis. Let ug contemplate the several groups of 
facts which point to this conclusion. 

In the last chapter (§ 2) we incidentally noted the extreme 
instability of nitrogenous compounds in generaL We saw 
that sundry of them are liable to explode on the slightest 
incentive — sometimes without any apparent cause ; and that 
of the rest, the great majority are very easily decomposed by 
heat, and by other substances. We shall perceive much 
significance in this general characteristic, when we join it 
with the fact, that the substances capable of initiating extensive 
molecular changes in the manner above described, are all 
nitrogenous ones. Yeast consists of vegetal cells containing 
nitrogen, — cells that grow by assimilating the nitrogenous 
matter contained in wort. Similarly, the " vinegar-plant," 
which so greatly facilitates the formation of acetic acid from 
alcohol, is a fungoid growth, that is doubtless, like others of 
its class, rich in nitrogenous compoimds. Diastase, by which 
the transformation of starch into sugar is effected, during 
the process of malting, is also a nitrogenous body. So too 
is a substance called synaptase — an albumenous principle 
contained in almonds, that has the power of working several 
metamorphoses in the matters associated with it. These 
nitrogenized compounds, like the rest of their family, are 
remarkable for the rapidity with which they decompose ; and 
the extensive changes produced by them in the accompanying 
oxy-hydro-carbons, are found to vary in their kinds accord- 
ing as the decompositions of the ferments vary in their 
stages. We have next to note, as having here a 

meaning for us, the chemical contrasts between those organ- 
isms which carry on their functions by the help of external 
forces, and those which carry on their functions by forces 
evolved from within. If we compare animals and plants, we 
see that whereas plants, characterized as a class by containing 
but little nitrogen, are dependent on the solar rays for their 
vital activities ; animals, the vital activities of which are not 


thus dependent, mainly consist of nitrogenous substances. 
There is one marked exception to this broad distinction, how- 
ever; and this exception is specially instructive. Among 
plants, there is a considerable group — the Fungi — many mem- 
bers of which, if not all, can live and grow in the dark ; and 
it is their peculiarity that they are very much more nitro- 
genous than other plants. Yet a third class of facts 
of like significance, is disclosed when we compare different 
portions of the same organisms. The seed of a plant contains 
nitrogenous substance in a far higher ratio than the rest of 
the plant ; and the seed differs from the rest of the plant in 
its ability to initiate, in the absence of light, extensive vital 
changes — the changes constituting germination. Similarly 
in the bodies of animals, those parts which carry on active 
functions are nitrogenous; while parts that are non- nitro- 
genous — 'as the deposits of fat — carry on no active functions. 
And we even find that the appearance of non-nitrogenous 
matter, throughout tissues normally composed almost wholly 
of nitrogenous matter, is accompanied by loss of activity : 
what is called fatty degeneration, being the concomitant of 
failing vitality. One more fact which serves to make 
still clearer the meaning of the foregoing ones, still remains — 
the fact, namely, that in no part of any organism where vital 
changes are going on, is nitrogenous matter wholly absent. 
It is common to speak of plants — or at least all parts of 
plants but the seeds — as non-nitrogenous. But they are only 
relatively so ; not absolutely. The quantity of albumenoid 
substance contained in the tissues of plants, is extremely small 
compared with the quantity contained in the tissues of ani- 
mals; but all plant-tissues which are discharging active 
Unctions, contain some albumenoid substance. In every 
living vegetal cell there is a certain part that contains nitro« 
gen. This part initiates those changes which constitute the 
development of the cell. And if it cannot be said that the 
primordial tdricle, as this nitrogenous part is called, is the 
worker of ail subsequent changes undergone by the cell, it 


nevertheless continues to be the part in which the independent 
activity is most marked. 

Looking at the evidence thus brought together, do we 
not get an insight into the part played by nitrogenous 
matter in organic changes P We see that nitrogenous com- 
pounds in general, are extremely prone to decompose : their 
decomposition often involving a sudden and great evolution 
of force. We see that the substances classed as ferments, 
whichy during their own molecular changes, set up molecular 
changes in the accompanying oxy-hydro-carbons, are all 
nitrogenous. We see that among classes of organisms, and 
among the parts of each organism, there is a relation between 
the amount of nitrogenous matter present and the amount of 
independent activity. And we see that even in organisms 
and parts of organisms where the activity is least, such 
changes as do take place are initiated by a substance contain- 
ing nitrogen. Does it not seem probable, then^ that these 
extremely unstable compounds, have everywhere the effect of 
communicating to the less unstable compounds associated 
with them, molecular movements towards a stable state, like 
those they are themselves undergoing P The changes which 
we thus suppose nitrogenous matter to produce in a body, 
are clearly analogous to those which we see it produce out of 
the body. Out of the body, certain oxy-hydro-carbons in con- 
tinued contact with nitrogenous matter, are transformed into 
carbonic acid and alcohol, and unless prevented the alcohol 
is transformed into acetic acid : the substances formed being 
thus more highly oxidized and more stable than the substances 
destroyed. In the body, these same oxy-hydro-carbons 
together with some hydro-carbons, in continued contact with 
nitrogenous matter, are transformed into carbonic acid and 
water : substances which are also more highly oxidized and 
more stable than those from which they residt. And since 
acetic acid is itself resolved by further oxidation into carbonic 
acid and water ; we see that the chief difference between the 
two cases, is, that the process is more completely effected in the 


body, than it is out of the body.* Thus, to cany further the 
simile used above, the atoms of hydro-carbons and oxy-hydro- 
carbons contained in the tissues, are^ like bricks on end, not in 
the stablest equilibrium, but still in an equilibrium so stable, 
that they cannot be overthrown by the chemical and thermal 
forces which the body brings to bear on them. On the other 
hand, being like similarly-placed bricks that have very nar- 
row ends, the nitrogenous atoms contained in the tissues are 
in so unstable an equilibrium that they cannot withstand 
these forces. And when these delicately-poised nitrogenous 
atoms fall into stable arrangements, they give impulses to 
the more firmly-poised non-nitrogenous atoms, which cause 
them also to fall into stable arrangements. It is a 

curious and significant fact, that in the arts, we not only 
utilize this same principle of initiating extensive changes 
among comparatively stable compounds, by the help of com- 
pounds much less stable; but we employ for the purpose 
compounds of the same general class. Our modem method 
of firing a gun, is to place in close proximity with the gun- 
powder which we wish to decompose or explode, a small por- 
tion of fulminating powder, which is decomposed or exploded 
with extreme facility ; and which, on decomposing, communi- 
cates the consequent molecular disturbance to the less-easily 
decomposed gunpowder. When we ask what this fulminating 
powder is composed of, we find that it is a nitrogenous salt. 

Thus various evidences point to the conclusion, that besides 
the molecular re-arrangements produced in organic matter by 
direct chemical action, there are others of kindred importance 
produced by indirect chemical action. Indeed, the inference 

♦ May it not be well to inquire whether alcohol is not, in a greater or less 
measure, transformed in the body into acetic acid ? If, when in contact with 
changing nitrogenous matter, in presence of oxygen, alcohol undergoes this 
transformation out of the body, it seems not improbable that it does so in the body 
—especially as the raised temperature which aids the change in the one case exists 
in the other. It would be out of place here to set down the sundry facts which 
countenance this hypothesis. I may say, however, that it apparently remoTes 
some of the difficulties which at present perplex the question. 


that some of the leading transformations occurring in the 
animal organism, are due to this so-called catalysis, appears 
necessitated by the general aspect of the facts ; apart from 
any such detailed interpretations as the foregoing. We know 
that various amylaceous and saccharine matters taken as food, 
are decomposed in their course through the body. We know 
that these matters do not become components of the tissues, 
but only of the fluids circulating through them ; and that 
thus their metamorphosis is not an immediate result of the 
organic activities. We know that their stability is such that 
the thermal and chemical forces to which they are exposed 
in the body, cannot alone decompose them. The only explan- 
ation open to ns, therefore, is that the transformation of these 
oxy-hydro-carbons, into carbonic acid and water, is due to 
communicated chemical action. 

§ 16. This chapter will have served its purpose if it has 
given a conception of the extreme modifiability of organic 
matter by surrounding agencies. Even did space permit, 
it would be needless to describe in detail the immeusely 
varied and complicated changes which the forces from mo- 
ment to moment acting on them, work in living bodies. 
Dealing with biology in its general principles, it concerns us 
only to noticQ^ how specially sensitive are the substances of 
which organisms are built up, to the varied influences that 
act upon organisms. And their special sensitiveness has been 
made sufficiently manifest, in the several foregoing sections. 


§ 17. Be-distributions of Matter, imply concomitant re- 
distributions of Motion. That which under one of its aspects 
we contemplate as an alteration of Arrangement among the 
parts of a body, is, under a correlative aspect, an alteration 
of arrangement among certain momenta whereby these parts 
are impelled to their new positions. At the same time that 
a force, acting differently on the different units of an aggre- 
gate, changes their relations to each other ; these units, re- 
acting differently on the different parts of the force, work 
equivalent changes in the relations of these to one another. 
Inseparably connected as they are, these two orders of phe- 
nomena are liable to be confounded together. It is very 
needful, however, to distinguish between them. In the last 
chapter, we took a rapid survey of the re-distributions which 
forces produce in organic matter ; and here we must take li 
like survey of the simultaneous re-distributions undergone by 
the forces. 

At the outset we are met by a difficulty. The parts of an 
inorganic mass undergoing re-arrangement by an incident 
force, are, in most cases, passive — do not complicate those 
necessary re-actions that result from their inertia, by other 
forces which they originate. But in organic matter, the 
re-arranged parts do not re-act in virtue of their inertia only : 
they are so constituted that the incident force usually sets up 


in them^ other actions which* are much more important 
Indeed^ what we may call the indirect re-actions thus caused, 
are so great in their amounts compared with the direct re- 
actions, that they quite obscure them. 

In strictness, these two kinds of re-action should not be 
dealt with together. The impossibility of separating them, 
however, compels us to disregard the distinction between 
them. Under the above general title, we must include both 
the immediate re-actions and those re-actious mediately 
produced, which are among the most conspicuous of vital 

§ 18. From organic matter, as from all other matter, 
incident forces call forth that re-action which we know as 
heat. More or less of molecular vibration almost necessarily 
results, when, to the forces at work among the molecules 
of any aggregate, other forces are added. Experiment 
abundantly demonstrates this in the case of inorganic 
masses ; and it must equally hold in the case of organic 
masses. In both cases the force which, more markr 

edly than any other, produces this thermal re-action, is that 
which causes the union of different substances with each 
other. Though inanimate bodies admit of being greatly 
heated by pressure and by the electric current, yet the 
evolutions of heat thus induced, are neither so common, nor 
in most cases so conspicuous, as those resulting from chemical 
combination. And though in animate bodies, there are 
doubtless certain amounts of heat generated by other actions ; 
yet these are all secondary to the heat generated by the 
action of oxygen on the substances composing the tissues and 
the substances contained in them. Here, however, 

we see one of the characteristic distinctions between inani- 
mate and animate bodies. Among the first, there are but 
few which ordinarily exist in a condition to evolve the heat 
caused by chemical combination; and such as are in this 
condition soon cease to be so, when chemical combination 


and genesis of heat once begin in them. Whereas among 
the second, there universally exists the ability, more or less 
decided, thus to evolve heat ; and the evolution of heat, in 
some cases, very slight and in no cases very great^ continues 
as long as they remain animate bodies. 

The relation between active change of matter and re-active 
genesis of atomic vibration, is clearly shown by the contrasts 
between different organisms, and between different states and 
parts of the same organism. In plants, the genesis of heat is 
extremely small, in correspondence with their extremely 
small production of carbonic acid : those portions only, as 
flowers and germinating seeds, in which considerable oxidation 
is going on, having a decidedly raised temperature. Among 
animals, we see that the hot-blooded are those which expend 
much force and respire actively. We see that though such 
creatures as insects are scarcely at all warmer thap the surround- 
ing air when they are still, they rise several degrees above it 
when they exert themselves ; and that in creatures like our- 
selves, which habitually maintain a heat much greater than 
that of their medium, exercise is accompanied by an ad- 
ditional production of heat, often to an inconvenient extent. 

This molecular agitation accompanying the molecular 
re*arrangements that are caused by oxygen taken into the 
animal organism, must result both from the union of oxygen 
with those nitrogenous matters of which the tissues are 
composed, and from its union with those non-nitrogenous 
matters which are diffused through the tissues. Just as much 
heat as would be caused by the oxidation of such matters 
out of the body, must be caused by their oxidation in the 
body. In the one case as in the other, the heat must be re- 
garded as a concomitant. Whether the distinction 
made by Liebig between nitrogenous substances as tissue- 
food, and non-nitrogenous substances as heat-food, be true or 
not in a narrower sense, it cannot be accepted in the sense 
that tissue-food is not also heat-food. Indeed he does not 
himself assert it in this sense. The ability of carnivorous 


animals to live and generate heat while consmning matter that 
is almost exclusively nitrogenous, to say nothing of the con- 
stant relation above shown between functional activity and the 
e\*olution of heat, suffices to prove that the nitrogenous com- 
pounds forming the tissues are heat-producers, as well as the 
non- nitrogenous compounds circulating among and through 
the tissues. But it is possible that this antithesis is not 

true even in the more restricted sense. It seems quite an 
admissible hypothesis that the hydro-carbons and oxy-hydro- 
carbons which, in traversing the system, are transformed by 
communicated chemical action, evolve during their transform* 
ation, not heat alone, but also other kinds of force. It may be 
that as the nitrogenous matter, while falling into more stable 
molecular arrangements, generates both that molecular agi- 
tation called heat, and such other molecular movements as are 
resolved into forces expended by the organism ; so, too, does 
the non-nitrogenous matter. Or perhaps the concomitants of 
this metamorphosis of non- nitrogenous matter, vary with the 
conditions. Heat alone may result when it is transformed 
while in the circulating fluids , but partly heat, and partly 
another force, when it is transformed in some active tissue that 
has absorbed it : just as coal, though producing little else but 
heat as ordinarily burnt, has its heat partially transformed into 
mechanical motion if burnt in a steam-engine furnace. In 
Such case, the antithesis of Liebig would be reduced to this ; 
—that whereas nitrogenous substance is tissue-food ioM as 
material for building-up tissue and as material for its function; 
non-nitrogenous substance is tissue-food only as material for 

There can be no doubt that this thermal re-action which 
chemical action from moment to moment produces in the body, 
is from moment to moment an aid to further chemical 
action. We before saw {First Principles, § 103) that a state 
of raised molecular vibration, is favourable to those re-dis- 
tributions of matter and motion which constitute Evolution. 
We saw that in organismis distinguished by the amount and 


rapidity of such re-distributions, this raised state of molecular 
vibration is conspicuous. And we here see that this raised 
state of molecular vibration, is itself a continuous consequence 
of the continuous molecular re-distributions it facilitates. 
The heat generated by each increment of chemical change> 
makes possible the succeeding increment of chemical change. 
In the body this connexion of phenomena is the same as we 
see it to be out of the body. Just as in a burning piece of 
wood, the heat given out by the portion actually combining 
with oxygen, raises the adjacent portion to a temperature at 
which it also can combine with oxygen ; so, in a living 
animal, the heat produced by oxidation of each portion of 
tissue, maintains the temperature at which the unoxidized 
portions can be readily oxidized. 

$ 19. Among the forces called foHh from organisms by 
re-action against the actions to which they are subject, is 
Light. Phosphorescence is in some few cases displayed by 
plants^-especially by certain fungi. Among animals it is 
comparatively common. All know that there are several 
kinds of luminous insects ; and many are familiar with the 
fact that luminosity is a characteristic of various marine 

Most of the evidence goes to show that this evolution of 
light, as well as the evolution of heat, is consequent on oxi- 
dation of the tissues. Light, like heat, is the expression of a 
raised state of molecular vibration : the difference between 
them being a difference in the rates of vibration. Hence by 
chemical action on substances contained in the organism, heat 
or light may be produced, according to the character of the 
resulting molecular vibrations. The inferepce that 

oxidation is the cause of this luminosity, does not, however, 
rest only on d priori grounds. It is supported by experi- 
mental evidence. In phosphorescent insects, the continuance 
of the light is found to depend on the continuance of respira- 
tion ; and any exertion which renders respiration more active, 


increases the brilliancy of the light. MoreoTer, by separating 
the luminous matter. Prof. Matteucci has shown that its 
emission of light is accompanied by absorption of oxygen 
and escape of carbonic acid. The phosphorescence 

of marine animals has been referred to other causes than 
oxidation. In some cases, however, it is, I think, explicable 
without assuming any more special agency. Considering that 
in creatures of the genus Noctiluca^ for example,* to which the 
phosphorescence most commonly seen on our own coasts is 
due, there is no means of keeping up a constant circtdation» 
we may infer that the movements of aerated fluids through 
their tissues, must be greatly affected by impulses received 
from without. Hence it may be that the sparkles visible at 
night when the waves break gently on the beach, or when an 
oar is dipped into the water, are called forth from these 
creatures by the concussion, not because of any unknown 
influence it excites, but because, being propagated through 
their delicate tissues, it produces a sudden movement of the 
fluids and a sudden increase of chemical action. Neverthe- 
less, in other phosphorescent animals inhabiting the sea, as 
in the Pyrosama and in certain Annelida^ light seems to be 
really produced, not by direct re-action on the action of 
oxygen, but by some indirect re-action involving a trans- 
formation of force. 

§ 20. The re-distributions of matter in general, are accom* 
panied by electrical disturbances; and there is abundant 
evidence that electricity is generated during those re-distri* 
butions that are ever taking place in organisms. Experi- 
ments have shown ^* that the skin and most of the internal 
membranes are in opposite electrical states ; '' and also that 
between differentj^internal organs, as the liver and the stomach, 
there are electrical contrasts — such contrasts being greatest 
where the processes going on in the compared parts are most 
unlike. It has been proved by M. du Bois-Reymcmd that 
when any point in the longitudinal section of a muscle is 


connected by a conductor with any point in its transverse 
section, an electric current is established ; and fiirther, that 
like results occur when nerves are substituted for muscles. 
The special causes of these phenomena have not yet been 
determined. Considering that the electric contrasts are most 
marked where active secretions are going on — considering, 
too, that while they do not exist between external parts 
which are similarly related to the vascular currents, they do 
exist between external parts which are dissimilarly related 
1^0 the vascular currents — and considering also that they 
are extremely diifficult to detect where there are no appre- 
ciable movements of fluids ; it may be that they are due 
simply to the friction of heterogeneous substances, which is 
universally a cause of electric disturbance. But whatever be 
the interpretation, the fact remains the same, that there is 
throughout the living organism, an unceasing production of 
differences between the electric states of different parts ; and 
consequently an unceasing restoration of electric equilibrium 
by the establishment of currents among these parts. 

Besides these general, and not conspicuous, electrical phe- 
nomena which appear to be common to all organisms, vegetal 
as well as animal, there are certain special and strongly 
marked, ones. I refer, of course, to those which have made 
the Torpedo and the Gymnotua objects of so much interest. 
In these creatures we have a genesis of electricity that is not 
incidental on the performance of their different functions by 
the different organs ; but one which is itself a function, 
having an organ appropriate to it. The character of this 
organ in both these fishes, and its largely-developed con-» 
nexions with the nervous centres, have raised the suspicion, 
which various experiments have thus far justified, that in it 
there takes place a transformatioi) of what we call nerve-force 
into the force known as electricity : this conclusion being 
more especially supported by the fact, that substances, such as 
morphia and strychnia, which are known to be powerfu 


nervous stimulants, greatly increase the violence and rapidity 
of the electric discharges. 

But whether general or special, and in whatever manner 
produced, these evolutions of electricity are among the 
re-actions of organic matter, called forth by the actions to 
which it is subject. Though these re-actions are not direct, 
but seem rather to be remote consequences of those changes 
wrought by external agencies on the organism, they are yet 
incidents in that general re-distribution of motion, which 
these external agencies initiate ; and as such must here be 

§ 21. To these known modes of motion, has next to bo 
added an unknown one. Heat, Light, and Electricity are 
emitted by inorganic matter when undergoing changes, as 
well as by organic matter. But there is a kind of force mani- 
fested in some classes of living bodies, which we cannot 
identify with any of the forces manifested by bodies that are 
not alive, — a force which is thus unknown, in the sense that 
it cannot be assimilated with any otherwise-recognized class. 
I allude to what is called nerve-force. 

This is habitually generated in all animals, save the lowest, 
by incident forces of every kind. The gentle and violent 
mechanical contacts, which in ourselves produce sensations 
of touch and pressure — the additions and abstractions of mole- 
cular vibration, which in ourselves produce sensations of 
heat and cold ; produce in all creatures that have nervous 
systems, certain nervous disturbances — disturbances which, 
as in ourselves, are either communicated to the chief nervous 
centre, and there constitute consciousness, or else result in 
merely physical processes that are set going elsewhere in the 
organism. In special parts distinguished as organs of sense, 
other external actions bring about other nervous re-actions ; 
that show themselves either as special sensations, or as ex- . 
citements which, without the intermediation of consciousness, 



beget actions in muscles or other organs. Besides 

neural discharges that follow the direct incidence of external 
forces, there are others ever being caused by the incidence of 
forces which, though originally external, have become internal 
by absorption into the organism of the agents exerting them. 
For thus may be classed those neural discharges that from 
moment to moment result from modifications of the tissues, 
wrought by substances carried to them in the blood. That 
the imceasing change of matter which oxygen and other 
agents produce throughout the system, is accompanied by a 
genesis of nerve-force, is shown by various facts ; — by the fact 
that nerve-force is no longer generated, if oxygen be with- 
held, or the blood prevented from circulating ; by the fact that 
when the chemical transformation is diminished, as during 
sleep with its slow respiration and circulation, there is a 
diminution in the quantity of nerve-force ; in the fact that an 
excessive expenditure of nerve-force, involves excessive re- 
spiration and circulation, and excessive waste of tissue. To 
these proofs that nerve-force is evolved in greater or less quan- 
tity, according as the conditions to rapid molecular change 
throughout the body, are well or ill fulfilled ; may be added 
proofs that certain special molecular actions, are the causes 
of these special re-actions. The effects of alcohol, ether, 
chloroform, and the vegeto-alkalies, put beyond doubt the 
inference, that the overthrow of molecular equilibrium by 
chemical affinity, when it occurs at certain places in the body, 
results in the overthrow of equilibrium in the nerves pro- 
ceeding from these places — ^results^ that is, in the propagation 
through these nerves, of the change called a nervous dis- 
charge. Indeed, looked at from this point of view, 
the two classes of nervous changes — the one initiated from 
without and the other from within — are seen to merge into 
one class. Both of them may be traced to metamorphosis of 
tissue. There can be little doubt that the sensations of 
touch and pressure, are consequent on accelerated changes of 
matter, produced by mechanical disturbance of the mingled 


floidfl and solids composing the parts affected. There is 
abundant evidence that the sensation of taste, is due to the 
chemical actions set up by particles which find their way 
through the membrane covering the nerves of taste ; for, as 
Prof. Graham points out, sapid substances all belong to the 
class of crystalloids, which are able rapidly to permeate 
animal tissue, while colloids, which cannot pass through 
animal tissue, are all insipid. Similarly with the sense of 
smell. Substances which excite this sense, are necessarily 
more or less volatile ; and their volatility being the result of 
their molecular mobility, implies that they have in a high 
degree, the power of getting at the olfactory nerves by pene- 
trating their mucous investment. Again, the facts which 
photography has familiarized us with, make it clear that 
those nervous impressions called colours, are primarily due 
to certain changes wrought by light in the substance of the 
retina. And though, in the case of hearing, we cannot so 
clearly trace the connexion of cause and effect ; yet as we see 
that the auditory apparatus is one fitted to intensify those 
vibrations constituting sound, and to convey them to a recep- 
tacle containing fluid in which nerves are immersed ; it can 
scarcely be doubted that the sensation of sound proximately 
results from atomic re-arrangements caused in these nerves 
by the vibrations of the fluid : knowing, as we do, that the 
re-arrangement of atoms is in all cases aided by agita- 
tion. Perhaps, however, the best proof that nerve- 
force, whether peripheral or central in its origin, results from 
chemical transformation, lies in the fact that most of the 
chemical agents which powerfully affect the nervous system, 
affect it whether applied at the centre or the periphery. Vari- 
ous acids, mineral and vegetal, are tonics — the stronger ones 
being usually the stronger tonics; and this which we call 
their acidity, implies a power in them of acting on the nerves 
of taste, while the tingling or pain that follows their absorp- 
tion through the skin, implies that the nerves of touch are 
acted on by them. Similarly with certain vegeto-alkalies 



whicli are peculiarly bitter. These by their bitterness, show 
that they affect the extremities of the nerves ; while by their 
tonic properties, they show that they affect the nervous 
centres — ^the most intensely bitter among them, strychnia, 
being the most powerful nervous stimulant. However true 
it may be that this relation is not a regular one, since opium, 
hashish, and some other drugs, which work marked effects on 
the brain, are not remarkably sapid—however true it may be 
that there are relations between particular substances and 
particular parts of the nervous system ; yet such instances 
do but qualify, without negativing, the general proposition. 
The truth of this proposition can scarcely be doubted when, 
to the evidence above given, is added the fact that various 
condiments and aromatic] drugs are given as nervous stimu- 
lants ; and the fact that anaesthetics, besides the general effects 
they produce when inhaled or swallowed, produce local effects 
of like kind when absorbed through the skia ; and the fact 
that ammonia, which in consequence of its extreme molecular 
mobility, so quickly and so violently excites the nerves be- 
neath the skin, as well as those of the tongue and the nose, 
is a rapidly-acting stimulant when taken internally. 

Whether we shall ever know anything more of this nerve- 
force, than that it is some species of molecular disturbance 
that is propagated from end to end of a nerve, it is impossi- 
ble to say. Whether a nerve is merely a conductor, which 
delivers at one of its extremities an impulse received at the 
other ; or whether, as some now think, it is itself a generator 
of force which is initiated at one extremity and accumulates 
in its course to the other extremity ; are also questions which 
cannot yet be answered. All we know is, that forces capable 
of working molecular changes in nerves, are capable of 
calling forth from them manifestations of activity — dis- 
charges of some force, which, though probably allied to elec- 
tricity, is not identical with it. And our evidence that nerve- 
force is thus originated, consists not only of such facts as the 
above, but also of more conclusive facts established by direct 


experiments on nerves— experiments which show that nerve- 
force is generated when the cut end of a nerve is either me- 
chanically irritated, or acted on by some chemical agent, or 
subject to the galvanic current — experiments which thus 
prove that nerve-force is liberated by whatever disturbs the 
molecular equilibrium of nerve-substance. And this is all 
which it is necessary for us here to understand. 

§ 22. The most important of these re-actions called forth 
from organisms by surrounding actions, remains to be noticed. 
To the above various forms of insensible motion thus caused, 
we have to add sensible motion. On the production of this 
mode of force, more especially depends the possibility of all 
vital phenomena. It is, indeed, usual to regard the power of 
generating sensible motion, as confined to one out of the two 
organic sub-kingdoms ; or, at any rate, as possessed by but 
few members of the other. On looking closer into the matter, 
however, we see that plant-life as well as animal-life, is imi- 
versally accompanied by certain manifestations of this power ; 
and that plant-life could not otherwise continue. 

Through the humblest, as well as through the highest, ve- 
getal organisms, there are ever going on certain re-distribu- 
tions of matter. In protophytes the migroscope shows us an 
internal transposition of parts, which when not active enough 
to be immediately visible, is proved to exist by the changes 
of arrangement that become manifest in the course of hours 
and days. In the individual cells of many higher plants, an 
active movement among the contained granules may be wit- 
nessed. And well-developed cryptogams in common with all 
phanerogams, exhibit this genesis of mechanical motion still 
more conspicuously in the circulation of sap. It might, in- 
deed, be concluded a priori, that through plants displaying 
much differentiation of parts, an internal movement must be 
going on ; since, without it, the mutual dependence of organs 
having unlike functions would seem impossible. Be- 

sides these motions of fluids kept up internally, plants, espe- 


cially of the lower orders, are able to move their external 
parts in relation to each other, and also to move about from 
place to place. Illustrations in abundance will occur to all 
students of recent Natural History — such illustrations as the 
active locomotion of the zoospores of many Algae, the rhyth- 
mical bendings of the OacillatoricB, the rambling progression 
of the DiatomacecB, In fact many of these smallest vegetals, 
and many of the larger ones in their early stages, display a 
mechanical activity not distinguishable from that of the 
simplest animals. Among well-organized plants, which are 
neve;r locomotive in their adult states, we still not unfre- 
quently meet with relative motions of parts. To such fami- 
liar cases as those of the Sensitive plant and the Yenus' 
fly-trap, many, others may be added. When its base is 
irritated, the stamen of the Berberry flower leans over and 
touches the pistil. If the stamens of the common wild Cistus 
be gently brushed with the finger, they spread themselves — 
bending away from the seed-vessel. And some of the orchid- 
flowers, as Mr Darwin has recently shown, shoot out masses 
of pollen on to the entering bee, when its trunk is thrust 
down in search of honey. 

Though the power of moving is not, as we see, a character- 
istic of animals alone, yet in them, considered as a class, it is 
manifested to an extent so marked, as practically to become 
one of their distinctive characters — indeed, we may say, their 
most distinctive character. For it is by their immensely 
greater ability to generate mechanical motion, that animals 
are enabled to perform those actions which constitute their 
visible lives ; and it is by their immensely greater ability to 
generate mechanical motion, that the higher orders of animals 
are most obviously distinguished from the lower orders. 
Though, on remembering the seemingly active movements of 
infusoria, some will perhaps question this last-named con- 
trast ; yet, on comparing the quantities of matter propelled 
through given spaces in given times, they will see that the 
momentum evolved is far less in the protozoa than in the 


teleozoa. These sensible motions of animals are effected 

by various organs under various stimuli. In the humblest 
formsy and even in some of the more developed ones which 
inhabit the water, locomotion results from the vibrations of 
cilia: the contractility resides in these waving hairs that 
grow from the surface. Some of the Acalephw^ and their 
allies the Polypes, move when mechanically irritated : the 
long pendant tentacle of a Phyealia is suddenly drawn up if 
touched ; and, as well as its tentacles, the whole body of 
a Hydra collapses if roughly handled, or jarred by some 
shock in its neighbourhood. In all the higher animals how- 
ever, and to a smaller degree in many of the lower, sensible 
motion is generated by a special tissue, under the special ex- 
citement of a neural discharge. Though it is not strictly true 
that such animals show no sensible motions otherwise caused ; 
since all of them have certain ciliated membranes, and since 
the circulation of fluid in them is partially due to osmotic and 
capillary actions ; yet, generally speaking, we may say that 
their movements are effected only by muscles that contract 
only through the agency of nerves. 

What special transformations offeree generate these various 
mechanical changes, we do not, in most cases, know. Those 
re-distributions of fluid, with the alterations of form sometimes 
caused by them, that result from osmose, are not, indeed, 
quite incomprehensible. Certain motions of plants which, 
like those of the " animated oat," follow contact with water, 
are easily interpreted ; as are also such other vegetal motions 
as those of the Touch-me-not, the Squirting Cucumber, and the 
Carpoholm. But we have as yet no clue to the mode in which 
molecular movement is transformed into the movement of 
masses, in animals. We cannot refer to known causes the 
rhythmical action of a Medusa's disc, or that slow decrease of 
bulk that spreads throughout the mass of an Alcyonium, when 
one of its component individuals has been irritated. Nor 
are we any better able to say how the insensible motion 
transmitted through a nerve, gives rise to sensible motion in 


a muscle. Ifc is true that Science has given to Art, several 
methods of changing insensible into sensible motion. By ap- 
plying heat to water we vaporize it ; and the movement of its 
expanding vapour, we transfer to solid matter ; but it is clear 
that the genesis of muscular movement is in no way analogous 
to this. The force evolved during chemical transformations 
in a galvanic battery, we communicate to a soft iron magnet 
through a wire coiled round it ; and it would be quite possi- 
ble, by placing near to each other several magnets thus 
excited, to obtain, through the attraction of each for its 
neighbours, an accumulated movement made up of their 
separate movements, and thus to mechanically imitate a mus- 
cular contraction ; but from what we know of organic mat- 
ter, and the structure of muscle, there is no reason to suppose 
that anything analogous to this takes place in it. We 

can, however, through ene kind of molecular change, produce 
sensible changes of aggregation such as possibly might, when 
occurring in organic substance, cause sensible motion in 
it : I refer to allotropic change. Sulphur, for example, as- 
sumes different crystalline and non-crystalline forms at dif- 
ferent temperatures ; and may be made to pass backwards 
and forwards from one form to another, by slight variations 
of temperature : undergoing each time an alteration of bulk. 
We know that this allotropism, or rather its analogue iso- 
merism, prevails among colloids — inorganic and organic. 
We also know that some of these metamorphoses among col- 
loids, are accompanied by visible re-arrangements : instance 
hydrated silicic acid, which, after passing from its soluble 
state to the state of an insoluble jelly, begins, in a few days, 
to contract, and to give out part of its contained water. Now, 
considering that such isomeric changes of organic as well as 
inorganic colloids, are often very rapidly produced by very 
slight causes, it seems not impossible that some of the colloids 
constituting muscle, may be thus changed by a nervous dis- 
charge — resuming their previous condition when the dis- 
charge ceases. And it is conceivable that by structural 


arrangements, minute sensible motions so caused, may bo ac« 
cumulated into large sensible motions. There is, however, 
no evidence to support this supposition. 

§ 23. But the truths vrhich it is here our business espe- 
cially to note, are quite independent of hypotheses or inter- 
pretations. It is sufficient for the ends we have in view, to 
observe that organic matter does exhibit these several conspi- 
cuous re-actions, when acted on by incident forces : it is not 
requisite that we should know how these re-actions originate. 

In the last chapter were set forth the several modes in 
which incident forces cause re-distributions of organic mat- 
ter ; and in this chapter have been set forth the several modes 
in which is manifested the motion accompanying this re-dis- 
tribution. There we contemplated imder its several aspects, 
the general fact, that in consequence of its extreme instability, 
organic matter xmdergoes extensive molecular re-arrange- 
ments, on very slight changes of conditions. And here we 
have contemplated under its several aspects, the correlative 
general fact, that during these) extensive molecular re-arrange- 
ments, there are necessarily evolved large amounts of force. 
In the one case the atoms of which organic matter consists, 
are regarded as changing from positions of unstable equili- 
brium to positions of stable equilibrium ; and in the other 
case they are regarded as giving out in their falls from 
unstable to stable equilibrium, certain momenta — ^momenta 
that may be manifested as heat, light, electricity, nerve- 
force or mechanical motion, according as the conditions 

I will add only that these evolutions of force are rigor- 
ously dependent on these changes of matter. It is a corol- 
lary from that primordial truth which, as we have seen, 
underlies all other truths, {First Principles^ §§ 76, 141,) 
that whatever amount of power an organism expends in 
any shape, is the correlate and equivalent of a power that 
was taken into it from without. On the one hand, it 


follows from the persistence of force, that each portion of 
mechanical or other energy which an organism exerts, im- 
plies the transformation of as much organic matter as con- 
tained this energy in a latent state. And on the other hand, 
it follows from the persistence of force that no such trans- 
formation of organic matter containing this latent energy 
can take place, without the energy being in one shape or 
other manifested. 



§ 24. To those who accept the general doctrine of Evolu- 
tion, it needs scarcely be pointed out that classifications are 
subjective conceptions, which have no absolute demarcations 
in Nature corresponding to them. They are appliances by 
which we limit and arrange the matters under investigation ; 
and so facilitate our thinking. Consequently, when we at- 
tempt to define anything complex, or make a generalization 
of facts other than the most simple, we can scarcely ever 
avoid including more than we intended, or leaving out some- 
thing that should be taken in. Thus it happens that on 
seeking a definition of Life, we have great difficulty in find- 
ing one that is neither more nor less than sufficient. Let 
us look at a few of the most tenable definitions that have 
been given. While recognizing the respects in which they 
are defective, we shall see what requirements a more com- 
plete one must fulfil. 

* This chapter and the following two chapters originally appeared in Part 
III. of the JMneiplea ofFsyehology : forming a preliminary which, though indis- 
pensahle to the argument there developed, was somewhat parenthetical. Haying 
now to deal with the general science of Biology hefore the more special one of 
^Psychology, it becomes possible to transfer these chapters to their proper place. 
They have been carefully revised. 


Sclielling said that Life is the tendency to individuation. 
This fommla, until studied, conveys little meaning. But it 
needs only to consider it as illustrated by the facts of develop- 
menty or by the contrasts between lower and higher forms of 
life, to recognize its value ; especially in respect of compre- 
hensiveness. As before shown, however, (First Prifictples, 
§ 66), it is objectionable, partly on the ground that it refers, 
not so much to the functional changes constituting Life, as to 
the structural changes of those aggregations of matter which 
manifest Life; and partly on the ground that it includes 
under the idea Life, much that we usually exclude from it : 
for instance— crystallization. 

The definition of Richerand, — " Life is a collection of 
phenomena which succeed each other during a limited time 
in an organized body,'* — is liable to the fatal criticism, that 
it equally applies to the decay which goes on after death. 
For this, too, is " a collection of phenomena which succeed 
each other during a limited time in an organized body." 

"Life," according to De Blainville, "is the two-fold 
internal movement of composition and decomposition, at once 
general and continuous." This conception is in some re- 
spects too narrow, and in other respects too wide. On the 
one hand, while it expresses what physiologists distinguish as 
vegetative life, it excludes those nervous and muscular 
functions which form the most conspicuous and distinctive 
classes of vital phenomena. On the other hand, it describes 
not only the integrating and disintegrating processes going on 
in a Kving body, but it equally well describes those going on 
in a galvanic battery ; which also exhibits a " two-fold in- 
ternal movement of composition and decomposition, at once 
general and continuous." 

Elsewhere, I have myself proposed to define Life as " the 
co-ordination of actions ; "* and I still incline towards this de- 
finition as one answering to the facts with tolerable precision. 

• See Westminster Beview for April, 1852. —Art. IV. "A Theory of Popu- 


It includes all organic changes, alike of the viscera, the 
limbs, and the brain. It excludes the great mass of inor- 
ganic changes ; which display little or no co-ordination. By 
making co-ordination the specific characteristic of vitality, 
it involves the truths, that an arrest of co-ordination is 
death, and that imperfect co-ordination is disease. More- 
over, it harmonizes with our ordinary ideas of life in its dif- 
ferent gradations : seeing that the organisms which we rank 
as low in their degree of life, are those which display but 
little co-ordination of actions ; and seeing that from these up 
to man, the recognized increase in degree of life corresponds 
with an increase in the extent and complexity of co-ordina- 
tion. But, like the others, this definition includes too much ; 
for it may be said of the Solar System, with its regularly- 
recurring movements and its self-balancing perturbations, 
that it, also, exhibits co-ordination of actions. And how- 
ever plausibly it may be argued that, in the abstract, the 
motions of the planets and satellites are as properly compre- 
hended in the idea of life, as the changes going on in a 
motionless, unsensitive seed ; yet, it must be admitted that 
they are foreign to that idea as commonly received, and 
as here to be formulated. 

It remains to add the definition since suggested by Mr 
G. H. Lewes — "Life is a series of definite and successive 
changes, both of structure and composition, which take place 
within an individual without destroying its identity." The 
last fact which this statement has the merit of bringing into 
view — ^the persistence of a living organism as a whole, in 
spite of the continuous removal and replacement of its parts 
— is important. But otherwise it may be argued, that since 
changes of structure and composition, though probably the 
cames of muscular and nervous actions, are not the muscular 
and nervous actions themselves, the definition excludes the 
more visible movements with which our idea of life is most 
associated ; and further, that in describing vital changes as 
a series, it scarcely includes the fact that manv of them, as 


Nutrition^ Circulation, Bespiration^ and Secretion, in their 
many subdivisions, go on simultaneously. 

Thus, however well each of these definitions expresses 
the phenomena of life under some of its aspects, no one of 
them is more than approximately true. It may turn out, that 
to find a formula which will bear every test is impossible. 
Meanwhile, it is possible to frame a more adequate formula 
than any of the foregoing. As we shall presently find, 
these all omit an essential peculiarity of vital changes in 
general — ^a peculiarity which, perhaps more than any other, 
distinguishes them from non- vital changes. Before specify- 
ing this peculiarity, however, it will be well to trace our way, 
step by step, to as complete an idea of Life as may be reached 
from our present stand-point : by doing which, we shall both 
see the necessity for each limitation as it is made, and ulti- 
mately be led to feel the need for a further limitation. 

And here, as the best mode of determining what are those 
general characteristics which distinguish vitality from non- 
vitality, we shall do well to compare the two most unlike 
kinds of vitality, and see in what they agree. Manifestly, 
that which is essential to Life must be that which is common 
to Life of all orders. And manifestly, that which is common 
to all forms of Life, will most readily be seen on contrasting 
those forms of Life which have the least in common, or ape 
the most unlike.* 

§ 25. Choosing assimilation, then, for our example of 
bodily life, and reasoning for our example of that life 
known as intelligence ; it is first to be observed, that they 
are both processes of change. Without change, food cannot 
be taken into the blood nor transformed into tissue : without 

• This paragraph replaces a sentence that, in The Principles of PayeMogy, 
referred to a preceding chapter on '•^ Method ; " in which the mode of procedure 
here indicated, was set forth as a mode to he systematically pursued in the choice 
of hypotheses. Should opportunity ever permit, this chapter on Method will he 
embodied, along with other matter on the same topic, m a General Introduction 
to Fii'at Ft'ificiples. 


change, thece can be no getting from premisses to conclusion. 
And it is this conspicuous manifestation of change, which 
forms the substratum of our idea of Life in generaL Doubt- 
less we see innumerable changes to which no notion of vital- 
ity attaches : inorganic bodies are ever imdergoing changes 
of temperature, changes of colour, changes of aggregation. 
But it will be admitted that the great majority of the phe- 
nomena displayed by inorganic bodies, are statical and not 
dynamical; that the modifications of inorganic bodies are 
mostly slow and unobtrusive ; that on the one hand, when 
we see sudden movements in inorganic bodies, we are apt to 
assume living^ agency, and on the other hand, when we see 
no movements in organic bodies, we are apt to assume death. 
From aU which considerations it is manifest, that be the 
requisite qualifications what they may, a definition of Life 
must be a definition of some kind of change or changes. 

On further comparing assimilation and reasoning, with a 
view of seeing in what respect the change displayed in both 
differs from non- vital change, we find that it differs in being 
not simple change, but change made up of successive changes. 
The transformation of food into tissue, involves mastication, 
deglutition, chjrmification, chylification, absorption, and those 
various actions gone through after the lacteal ducts have 
poured their contents into the blood. Carrjdng on an argu- 
ment necessitates a long chain of states of consciousness; 
each implying a change of the preceding state. Inorganic 
changes, however, do not in any considerable degree exhibit 
this peculiarity. It is true that from meteorologic causes, 
inanimate objects are daily, sometimes hourly, undergoing 
modifications of temperature, of bulk, of hygrometric and 
electric condition. Not only, however, do these modifications 
lack that conspicuousness and that rapidity of succession 
which vital ones possess, but vital ones form an additional 
series. Living as well as not-living bodies are affected 
by atmospheric influences ; and beyond the changes which 
these produce, living bodies exhibit other changes, more nu- 


merous and more marked. So that though organic change 
is not rigorously distinguished from inorganic change by 
presenting successive phases — though some inanimate objects, 
as watches, display phases of change both quick and nu- 
merous — though all objects are ever undergoing change of 
some kind, visible or invisible — though there is scarcely any 
object which does not, in the lapse of time, imdergo a con- 
siderable amoimt of change that is fairly divisible into phases; 
yet, vital change so greatly exceeds other change in its dis- 
play of varying phases, that we may consider this as prac- 
tically one of its characteristics. Life, then, as thus roughly 
differentiated, may be regarded as change presenting succes- 
, sive phases ; or otherwise, as a series of changes. And it 
should be observed, as a fact in harmony with this concep- 
tion, that the higher the life the more conspicuous the varia- 
tions. On comparing inferior with superior organisms, these 
last will be seen to display more rapid changes, or a more 
lengthened series of them, or both. 

Contemplating afresh our two tjrpical phenomena, we 
may see that vital change is further distinguished from non- 
vital change, by being made up of many eimuttaneous changes. 
Assimilation is not simply a series of actions, but includes 
many actions going on together. During mastication the 
stomach is busy with the food already swallowed ; on which 
it is both pouring out solvent fluids and expending muscular 
efforts. While the stomach is still active, the intestines are 
performing their secretive, contractile, and absorbent func- 
tions ; and at the same time that one meal is being digested, 
the nutriment obtained from a previous meal is undergoing 
that transformation into tissue which constitutes the final act 
of assimilation. So also is it, in a certain sense, with mental 
changes. Though the states of consciousness which make up 
an argument occur in series, yet, as each of these states is 
complex — implies the simultaneous excitement of those many 
faculties by which the perception, of any object or relation 
has been effected; it is obvious that each such change in 


consciousness implies many component changes. In 

this respect too, however, it must be admitted that the 
distinction between animate and inanimate is not precise. 
No mass of dead matter can have its temperature altered, 
without at the same time undergoing an alteration in bulk, 
and sometimes also in hygrometric state. An inorganic 
body cannot be oxidized, without being at the same time 
changed in weight, colour, atomic arrangement, temperature, 
and electric condition. And in some vast and mobile aggre- 
gates like the sea, the simultaneous as well as the successive 
changes displayed, outnumber those going on in an animal. 
Nevertheless, speaking generally, a living thing is distin- 
guished from a dead thing, by the multiplicity of the changes 
at any moment taking place in it. Add to which, that by 
this peculiarity, as by the previous one, not only is the vital 
more or less clearly marked off from the non- vital ; but 
creatures possessing high vitality are marked off from those 
possessing low vitality. It needs but to contrast the many 
organs co-operating in a mammal, with the few in a polype, 
to see that the actions which are progressing together in the 
body of the first, as much exceed in number the actions pro- 
gressing together in the body of the last, as these do those 
in a stone. As at present analyzed, then, Life consists of 
simultaneous and successive changes. 

Continuing the comparison, we next find that vital changes, 
both visceral and cerebral, differ from other changes in their 
heterogeneity. Neither the simultaneous acts nor the serial 
acts, which together constitute the process of digestion, are 
at all alike. The states of consciousness comprised in any 
ratiocination are not repetitions of each other, either in com- 
position or in modes of dependence. Inorganic processes, on 
the other hand, even when like organic ones in the number 
of the simultaneous and successive changes they involve, are 
unlike them in the homogeneity of these changes. In the 
case of the sea, just referred to, it is observable that count- 
less as are the actions at any moment going on, they are 



mostly mechanical actions that are to a great degree similar ; 
and in this respect widely differ from the actions at any mo- 
ment taking place in an organism : which not only belong to 
the several classes, mechanical, chemical, thermal, electric, but 
present under each of these classes, innumerable unlike actions. 
Even where life is nearly simulated, as by the working of a 
steam-engine, we may see that considerable as is the number 
of simultaneous changes, and rapid as are the successive ones, 
the regularity with which they soon recur in the same order 
and degree, renders them unlike those varied changes exhi- 
bited by a Kving creature. Still, it will be found that 
this peculiarity, like the foregoing ones, does not divide the 
two classes of changes with precision ; inasmuch as there are 
inanimate things which exhibit considerable heterogeneity of 
change : for instance, a cloud. The variations of state which 
this undergoes, both simultaneous and successive, are many 
and quick ; and they differ widely from each other both in 
quality and quantity. At the same instant there may occur 
in a cloud, change of position, change of form, change of 
size, change of density, change of colour, change of tem- 
perature, change of electric state ; and these several kinds of 
change are continuously displayed in different degrees and 
combinations. Yet notwithstanding this, when we consider 
that very few inorganic objects manifest heterogeneity of 
change in a marked manner, while all organic objects mani- 
fest it ; and fiirther, that in ascending from^low to high forms 
of life, we meet with an increasing variety in the kinds and 
amounts of changes displayed; we see that there is here 
a further leading distinction between organic and inorganic 
actions. According to this modified conception, then, Life is 
made up of heterogeneous changes both simultaneous and 

If now we look for some point of agreement between the 
assimilative and logical processes, by which they are distin- 
guished from those inorganic processes that are most like 
them in the heterogeneity of the simultaneous and successive 


changes they comprise, we discoyer that they are distinguish* 
ed by the combination subsisting among their constituent 
changes. The acts that make up digestion are mutually de- 
pendent. Those composing a train of reasoning are in close 
connection. And generally, it is to be remarked of vital 
changes, that each is made possible by all, and all are affected 
by each. Respiration, circulation, absorption, secretion, in 
their many sub-divisions, are bound up together. Muscular 
contraction involves chemical change, change of temperature, 
and change in the excretions. Active thought influences the 
operiktions of the stomach, of the heart, of the kidnoys. But we 
miss this union among inorganic processes. Life-like as may 
seem the action of a volcano in respect of the heterogeneity 
of its many simultaneous and successive changes, it is not life- 
like in respect of their combination. Though the chemical, 
mechanical, thermal, and electric phenomena exhibited, have 
some inter-dependeiice ; yet the emission of stones, mud, lava* 
flame, ashes, smoke, steam, usually takes place irregularly ia 
quantity, order, intei^als, and mode of conjunction. Even 

here, however, it cannot be said that inanimate things pre- 
sent no parallels to animate ones. A glacier may be instanced 
as showing nearly as much combination in its changes as a 
plant of the lowest organization. It is ever growing and 
ever decaying ; and the rates of its composition and decom- 
position preserve a tolerably constant ratio. It moves ; and 
its motion is in immediate dependence on its thawing. It 
emits a torrent of water, which, in common with its motion, 
undergoes annual variations, as plants do. During part 
of the year the surface melts and freezes alternately ; and 
on these changes are dependent the variations in movement, 
and in efflux of water. Thusi we have growth, decay, changes 
of temperature, changes of consistence, changes of velocity, 
changes of excretion, all going on in connexion ; and it may 
be as truly said of a glacier as of an animal, that by cease- 
less integration and disintegration it gradually undergoes an 
entire change of substance without losing i(s individuality. 



This exceptional instance, however, will scarcely be held to 
obscure that broad distinction from inorganic processes, 
which organic processes derive from the combination among 
their constituent changes. And the reality of this distinction 
becomes yet more manifest when we find that, in common 
with previous ones, it not only marks ofiF the living from the 
not-living, but also things which live little from things which 
live much. For while the changes going on in a plant or a 
zoophyte are so imperfectly combined that they can continue 
after it has been divided into two or more pieces^ the com* 
bination among the changes going on in a mammal is so 
close that no part cut off from the rest can live, and any con- 
siderable disturbance of one function causes a cessation of the 
others. Life, therefore, as we now regard it, is a com- 
bination of heterogeneous changes, both simultaneous and 

Once more looking for a characteristic common to these 
two kinds of vital action, we perceive that the combinations 
of heterogeneous changes which constitute them, differ from 
the few combinations which they otherwise resemble, in re- 
spect of definiteness. The associated changes going on in a 
glacier, admit of indefinite variation. Under a conceivable 
alteration of climate, its thawing and its progression may be 
stopped for myriads of years, without disabling it from again 
displajring these phenomena under appropriate conditions. 
By a geological convulsion, its motion may be arrested with- 
out an arrest of its thawing ; or by an increase in the in- 
clination of the surface it slides over, its motion may be 
accelerated without accelerating its rate of dissolution. 
Other things remaining the same, a more rapid deposit of 
snow may cause an indefinite increase of bulk ; or, conversely 
the accretion may entirely cease, and yet all the other actions 
continue until the mass disappears. Here, then, the combina- 
tion has none of that definiteness which, in a plant, marks 
the mutual dependence of assimilation, respiration, and cir- 
culation; much less has it that definiteness seen in the 


mutual dependence of tlie chief animal functions : no one of 
which can be varied without varying the rest: no one of 
which can go on unless the rest go on. It is this definiteness 
of combination which distinguishes the changes occurring 
in a living body from those occurring in a dead one. Decom- 
position exhibits both simultaneous and successive changes, 
which are to some extent heterogeneous, and in a sense com- 
bined ; but they are not combined in a definite manner. They 
vary according as the surrounding medium is air, water, or 
earth. They alter in nature with the temperature. If the local 
conditions are unlike, they progress differently in different 
parts of the mass, without mutual influence. They may end in 
producing gases, or adipocire, or the dry substance of which 
mummies consiBt. They may occupy a few days, or thousands 
of years. Thus, neither in their simultaneous nor in their suc- 
cessive changes, do dead bodies display that definiteness of 
combination which characterizes living ones. It is 

true that in some inferior creatures the cycle of successive 
changes admits of a certain indefiniteness — that it may 
be apparently suspended for a long period by desiccation or 
freezing; and may afterwards go on as though there had 
been no breach in its continuity. But the circumstance 
that only a low order of life permits the cycle of its changes 
to be thus modified, serves but to suggest that, like the pre- 
vious characteristics, this characteristic of definiteness in its 
combined changes, distinguishes high vitality from low vital- 
ity, as it distinguishes low vitality from inorganic processes. 
Hence, our formula as further amended reads thus : — ^Life is 
a definite combination of heterogeneous changes, both simul- 
taneous and successive. 

Finally, we shall still better express*the facts, if, instead of 
saying a definite combination of heterogeneous changes, we 
say the definite combination of heterogeneous changes. As 
it at present stands, the definition is defective both in allow* 
ing that there may be other definite combinations of hetero- 
geneous changes, and in directing attention to the hetero- 



geneons changes rather than to the definiteness of their 
combination. Just as it is not so much its chemical elements 
which constitute an organism, as it is the arrangement of 
them into special tissues and organs ; so it is not so much its 
heterogeneous changes which constitute Life, as it is the de- 
finite combination of them. Observe what it is that ceases 
when life ceases. In a dead body there are going on hetero- 
geneous changes, both simultaneous and successive. What 
then has disappeared? The definite combination has dis- 
appeared. Mark, too, that however heterogeneous the simul- 
taneous and successive changes exhibited by an inorganic 
object, as a volcano, we much less tend to think of it as 
living, than we do a watch or a steam-engine, which, though 
displaying homogeneous changes, displays them definitely 
combined. So dominant an element is this in our idea of 
Life, that even when an object is motionless, yet, if its part«( 
be definitely combined, we conclude either that it has had 
life, or has been made by something having Ufe. Thus then, 
we conclude that Life is — the definite combination of hetero- 
geneous changes, both simultaneous and successive. 

% 26. Such is the conception at which we arrive without 
changing our stand-point. It is, however, an incomplete 
conception. This ultimate formula (which is to a consider- 
able extent identical with one above given — " the co-ordina- 
tion of actions ;'' seeing that '^ definite combination" is 
synonymous with "co-ordination," and "changes both si- 
multaneous and successive" are comprehended under the 
term " actions ; " but which differs from it in specifying the 
fact, that the actions or changes are " heterogeneous ") — ^this 
ultimate formula, I say, is after all but proximately correct. 
It is true that it does not fail by including the growth of 
a crystal ; for the successive changes this implies cannot be 
called heterogeneous. It is true that the action of a galvanio 
battery is not comprised in it ; since here, too, heterogeneity 
is not exhibited by the successive changes. It is true that by 


this same qualification the motions of the Solar System are 
excluded ; as are also those of a watch and a steam-engine. 
It is true, moreover, that while, in virtue of their heteroge* 
neity, the actions going on in a cloud, in a volcano, in a 
glacier, fulfil the definition ; they fall short of it in lacking 
definiteness of combination. It is further true that this de- 
finiteness of combination, distinguishes the changes taking 
place in an organism during life, from those which commence 
at death. And beyond all this it is true that, as well as 
serving to mark off, more or less clearly, organic actions from 
inorganic actions, each member of the definition serves to 
mark off the actions constituting high vitality from those 
constituting low vitality ; seeing that life is high in propor- 
tion to the number of successive changes occurring between 
birth and death ; in proportion to the number of simulta'heous 
changes ; in proportion to the heterogeneity of the changes ; 
in proportion to the combination subsisting among the 
changes ; and in proportion to the definiteness of their com- 
bination. Nevertheless, answering though it does to so 
many requirements, this definition is essentially defective. 
It does not convey a complete idea of the thing contem- 
plated. The definite combination of heterogeneous changes, both 
simultaneous and successive, is a formula which fails to call 
up an adequate conception. And it fails from omitting the 
most distinctive peculiarity — the peculiarity of which we 
have the most familiar experience, and with which our notion 
of Life is, more than with any other, associated. It remains 
now to supplement the definition by the addition of this 



I 27. Wb habitually distinguisli between a live object 
and a dead one, by observing whether a change which we 
make in the surrounding conditions, or one which Nature 
makes in them, is or is not followed by some perceptible change 
in the object. By discovering that certain things shrink when 
touched, or fly away when approached, or start when a noise 
is made, the child first roughly discriminates between the 
living and the not-living; and the man when in doubt 
whether an animal he is looking at is dead or not, stirs it 
with his stick ; or if it be at a distance, shouts, or throws a 
stone at it. Vegetal and animal life are alike primarily 
recognized by this process. The tree that puts out leaves 
when the spring brings a change of temperature, the flower 
which opens and closes with the rising and setting of the 
sun, the plant that droops when the soil is dry, and re-erects 
itself when watered, are considered alive because of these in- 
duced changes ; in common with the zoophyte which contracts 
on the passing of a cloud over the sun, the worm that comes to 
the surface when the ground is continuously shaken, and the 
hedgehog that rolls itself up when attacked. 

Not only, however, do we habitually look for some response 
when an external stimulus is applied to a living organism, 
but we perceive a fitness in the response. Dead as well as 
living things display changes under certain changes of con- 


dition : instance, a lump of carbonate of soda that effervesces 
when dropped into sulphuric acid ; a cord that contracts 
when wetted ; a piece of bread that turns brown when held 
near the fire. But in these cases, we do not see a connexion 
between the changes undergone, and the preservation of the 
things that undergo them ; or, to avoid any teleological im- 
plication — ^the changes have no apparent relations to future 
external events which are sure or likely to take place. In 
vital changes, however, such relations are manifest. Light 
being necessary to vegetal life, we see in the action of a 
plant which, when much shaded, grows towards the unshaded 
side, an appropriateness which we should not see did it grow 
otherwise. Evidently the proceedings of a spider, which 
rushes out when its web is gently shaken and stays within 
when the shaking is violent, conduce better to the obtainment 
of food and the avoidance of danger than were they reversed* 
The fact that we feel surprise when, as in the case of a bird fas- 
cinated by a snake, the conduct tends towards self-destruction, 
at once shows how generally we have observed an adaptation 
of living changes to changes in surrounding circumstances. 

Note further the kindred truth, rendered so familiar by 
infinite repetition that we forget its significance, that there 
is invariably, and necessarily, a conformity between the vital 
functions of any organism, and the conditions in which it is 
placed — ^between the processes going on inside of it, and the 
processes going on outside of it. We know that a fish can- 
not live in air, or a man in water. An oak growing in the 
ocean, and a seaweed on the top of a hill, are incredible 
combinations of ideas. We find that every animal is limited 
to a certain range of climate ; every plant to certain zones of 
latitude and elevation. Of the marine flora and fauna, each 
species is found exclusively between such and such depths. 
Some blind creatures flourish only in dark caves ; the limpet 
only where it is alternately covered and uncovered by the 
tide ; the red-snow alga rarely elsewhere than in the arctic 
regions or among alpine peaks. 


Qrouping together the cases first named, in which a parti- 
cular change in the circumstances of an organism is followed 
by a particular change in it, and the cases last named, in 
which the constant actions occurring within an organism im- 
ply some constant actions occurring without it ; we see that 
in both^ the changes or processes displayed by a living body 
are specially related to the changes or processes in its en- 
vironment. And here we have the needful supplement to 
our conception of Life. Adding this all-important charac- 
teristic, our conception of Life becomes — The definite com- 
bination of heterogeneous changes, both simultaneous and 
successive, in correspondence mth external co-extstencea and 
sequences. That the full significance of this addition may be 
seen, it will be necessary to glance at the correspondence 
under some of its leading aspects.* 

§ 28. Neglecting minor requirements, tne actions going 

* Speakings of '* the general idea of life,** M. Comte sayt :-~*' Cette id^ sop- 
pose, en effet, non-seulement celle d*un etre organist de mani^re li comporter 
r^tat yital, mais aussi celle, non moins indispensable, d*un certain ensemble 
d'influences ext^rienre propres k son accomplissement. Une telle harmonie entre 
r^tre Tivant et le mUim correspondant, caracterise eyidemment la condition fon- 
damentale de la Tie." Commenting on de Blainyille's definition of life, which he 
adopts, he says : — '* Cette luminense definition ne me parait laisser rien d'impor- 
tant & d^sirer, si ce n'est nne indication plus directe et plus explicite de ces deux 
conditions fondamentales co-relatives, necessairement inseparables de T^tat viyant, 
im wrganUme determine et un milieu convenable/' It is strange that M. Comte 
Bhould have thus recognized the necessity of a harmony between an organism and 
its environment, as a condition essential to life, and should not have seen that the 
continuous maintenance of such inner actions as will counterbalance outer actions, 
cofutitutes life. It is the more strange that he should have been so near this 
truth and yet missed it, since, besides his wide range of thought, M. Comte is 
often remarkable for his clear intuitions. Lest by saying this, I should deepen a 
misconception into which some have fallen, let me take the opportunity of stating, 
that though I believe some of M. Comte's minor generalizations to be true, and 
though I recognize the profundity of many incidental observations he makes, I 
by no means accept his system. Those general doctrines in which I agree with 
him, are those which he holds in common with sundry other thinkers. With all 
those general doctrines which are distinctive of his philosophy, I disagree — with 
all those at least that I have definite knowledge of; for beyond the first half of 
his " Course of Positive Philosophy," I know his opinions only by hearsay. 


on in a plant pre-*8uppo6e a surrounding medium containing 
at least carbonic acid and water, together with a due supply 
of light and a certain temperature. Within the leaves 
carbon is being assimilated and oxygen given off; without 
them^ is the gas from which the carbon is abstracted, and the 
imponderable agents that aid the abstraction. Be the nature 
of the process what it may, it is clear that there are external 
elements prone to undergo special re-arrangements imder 
special conditions. It is clear that the plant in sunshine 
presents these conditions and so effects these re-arrange- 
ments. And thus it is clear that the changes which consti- 
tute the plant's life, are in correspondence with co-existences 
in its environment. 

If, again, we ask respecting the lowest protozoon, how 
it lives ; the answer is, that while on the one hand its sub* 
stance is ever undergoing oxidation, it is on the other hand 
ever absorbing nutriment ; and that it may continue U) exist, 
the assimilation must keep pace with, or exceed, the oxidation. 
If further we ask imder what circumstances these combined 
changes are possible; there is the obvious reply, that the 
medium in which the protozoon is placed, must contain oxy- 
gen and food — oxygen in such quantity as to produce some 
disintegration ; food in such quantity as to permit that dis- 
integration to be made good. In other words— the two 
antagonistic processes taking place internally, imply the pre- 
sence externally of materials having affinities that can give 
rise to these processes. 

Leaving those lowest animal forms revealed by the mi- 
croscope, which simply take in through their surfaces the 
nutriment and oxygenated fluids coming in contact with 
them, we pass to those somewhat higher forms which have 
their tissues partially specialized into assimilative and re- 
spiratory. In these we see a correspondence between certain 
actions in the digestive sac, and the properties of certain sur- 
rounding bodies. That a creature of this order may continue 
to live, it is necessary not only that there be masses of sub- 


stance in the environment capable of transformation into its 
own tissue ; but that the introduction of these masses into its 
stomach, shall be followed by the secretion of a solvent fluid 
that will reduce them to a fit state for absorption. Special 
outer properties must be met by special inner properties. 

When, from the process by which food is digested, we 
turn to the processes by which it is seized, we perceive the 
same general truth. The stinging and contractile power of 
a polype's tentacle, correspond to the sensitiveness and 
strength of the creatures serving it for prey. Unless that 
external change which brings one of these creatures in con- 
tact with the tentacle, were quickly followed by those inter- 
nal changes which result in the coiling and drawing up of 
the tentacle, the polype would die of inanition. The funda- 
mental processes of integration and disintegration within it, 
would get out of correspondence with the agencies and pro- 
cesses without it ; and the life would cease. 

Similarly, it may be shown that when the creature be- 
comes so large that its tissue cannot be efficiently supplied 
with nutriment by mere absorption through its limiting 
membranes, or duly oxygenated by contact with the fluid 
that bathes its surface, there arises a necessity for a circu- 
latory system by which nutriment and oxygen may be dis- 
tributed throughout the mass ; and the functions of this sys- 
tem, being subsidiary to the two primary functions, form 
links in the correspondence between internal and external ac- 
tions. The like is obviously true of all those subordinate 
functions, secretory and excretory, that facilitate oxidation 
and assimilation — ^functions in which we may trace, both co- 
temporaneous changes answering to co-existences in the en- 
vironment, and successive changes answering to those changes 
of composition, of temperature, of light, of moisture, of pres- 
sure, which the environment imdergoes. 

Ascending from the visceral actions to the muscular atid 
nervous actions, we find the correspondence displayed in a 
manner still more obvious. Every act of locomotion implies 


the expenditure of certain internal mechanical forces, adapted 
in amounts and directions to balance or out-balance certain 
external ones. The recognition of an object is impossible 
without a harmony between the changes constituting per- 
eeption, and particular properties co-existing in the environ* 
ment. Escape from enemies supposes motions within the 
organism, related in kind and rapidity to motions without it. 
Destruction of prey requires a particular combination of sub- 
jective actions, fitted in degree and succession to overcome a 
group of objective ones. And so with those countless au- 
tomatic processes exemplified in works on animal instinct. 

In the highest order of vital changes, the same fact is 
equally manifest. The empirical generalization that guides 
the farmer in his rotation of crops, serves to bring his actions 
into concord with certain of the actions going on in plants 
and soil. The rational deductions of the educated navigator 
who calculates his position at sea, constitute a series of mental 
acts by which, his proceedings are conformed to surrounding 
circumstances. Alike in the simplest inferences of the child, 
and the most complex ones of the man of science, we find a 
correspondence between simultaneous and successive changes 
in the organism, and co-existences and sequences in its envi- 

§ 29. This general formula, which thus includes the lowest 
vegetal processes as well as the highest manifestations of hu- 
man intelligence, will perhaps call forth some criticisms which 
it is desirable here to meet. 

It may be thought that there are still a few inorganic ac- 
tions included in the definition ; as for example that displayed 
by the mis-named storm-glass. The feathery crystallization 
which, on a certain change of temperature, takes place in the 
solution contained by this instrument, and which afterwards 
dissolves to reappear in new forms under new conditions, may 
be held to present simultaneous and successive changes that 
are to some extent heterogeneous, that occur with some dc- 


finiteness of combination, and, above all, occur in correspond- 
ence with external changes. In this case vegetal life is sim- 
ulated to a considerable extent ; but it is fnerely simulated. 
The relation between the phenomena occurring in the storm- 
glass and in the atmosphere respectively, is really not a cor- 
respondence at all, in the proper sense of the word. Outside 
there is a certain change ; inside there is a change of atomic 
arrangement. Outside there is another certain change ; in- 
side there is another change of atomic arrangement. But 
subtle as is the dependence of each internal upon each ex- 
ternal change, the connexion between them does not, in the 
abstract, differ from the connexion between the motion of a 
straw and the motion of the wind that disturbs it. In either 
case a change produces a change, and there it . ends. The 
alteration wrought by some environing agency on an inani- 
mate object, does not tend to induce in it a secondary altera- 
tion, that anticipates some secondary alteration in the en- 
vironment. But in every living body there is a tendency 
towards secondary alterations of this nature ; and it is in 
their production that the correspondence consists. The dif- 
ference may be best expressed by symbols. Let A be a 
change in the environment ; and B some resulting change 
in an inorganic mass. Then A having produced B, the ac-^ 
tion ceases. Though the change A in the environment, is 
followed by some consequent change ci in it ; no parallel se- 
quence in the inorganic mass simultaneously generates in it 
some change h that has reference to the change a. But if we 
take a living body of the requisite organization, and let the 
change A impress on it some change C ; then, while in the 
environment A is occasioning a, in the living body will 
be occasioning c : of which a and c will show a certain con- 
cord in time, place, or intensity. And while it is in the con- 
tinuous production of such concords or correspondences that 
Life consists, it hhy the continuous production of them that 
Life is maintained. 

The further criticism that may be expected, concerns cer- 


tain yerbal imperfections in the definition, whicli it seems 
impossible to avoid. It may be fairly urged that the word 
correspondence will not include^ without straining, the yarious 
relations to be expressed by it. It may be asked : — How can 
the continuous processes of assimilation and respiration, eor« 
respond with the co-existence of food and oxygen in the en- 
vironment ? or again : — How can the act of secreting some 
defensive fluid, correspond with some external danger which 
may never occur ? or again : — How can the dynamical phe- 
nomena constituting perception, correspond with the statical 
phenomena of the solid body perceived ? The only reply to 
these questions, is, that we have no word sufficiently general 
to comprehend all forms of this relation between the organ- 
ism and its medium, and yet sufficiently specific to convey an 
adequate idea of the relation ; and that the word correspond* 
ence seems the least objectionable. The fact to be expressed 
in aU cases, is, that certain changes, continuous or discon* 
tinuous, in the organism, are connected after such a manner 
that, in their amounts, or variations, or periods of occurrence, 
or modes of succession, they have a reference to external ac- 
tions, constant or serial, actual or potential — a reference such 
that a definite relation among any members of the one group, 
implies a definite relation among certain members of the 
other group ; and the word correspondence appears the best 
fitted to express this fact. 

§ 30. The presentation of the phenomena under this ge- 
neral form, suggests how our definition of Life may be reduced 
to its most abstract shape ; and perhaps its best shape. By 
regarding the respective elements of the definition as relations, 
we avoid both the circumlocution and the verbal inaccuracy ; 
and that we may so regard them with propriety is obvious. 
If a ereature's rate of assimilation is increased in consequence 
of a decrease of temperature in the environment ; it is that 
the relation between the food consumed and heat produced, is 
so re-adjusted by multiplying both its members, that the 


altered relation in the surrounding medium between the 
quantity of heat absorbed from, and radiated to, bodies of a 
given temperature, is counterbalanced. If a sound or a scent 
wafted to it on the breeze, prompts the stag to dart away 
from the deer-stalker ; it is that there exists in its neighbour- 
hood a relation between a certain sensible property and cer- 
tain actions dangerous to the stag, while in its organism 
there exists an adapted relation between the impression this 
sensible property produces, and the actions by which danger 
is escaped. If inquiry has led the chemist to a law, enabling 
him to tell how much of any one element will combine with 
so much of another ; it is that there has been established 
in him specific mental relations, which accord with specific 
chemical relations in the things around. Seeing, then, that in 
all cases we may consider the external phenomena as simply 
in relation, and the internal phenomena also as simply in re- 
lation ; the broadest and most complete definition of Life will 
be — The continuous adjustment of internal relations to external 

While it is simpler, this modified formula has the further 
advantage of being somewhat more comprehensive. To say 
that it includes not only those definite combinations of simul- 
taneous and successive changes in an organism, which cor- 
respond to co-existences and sequences in the environment, 
but also those structural arrangements which enable the or- 
ganism to adapt its actions to actions in the environment, 
may perhaps be going too far ; for though these structural 
arrangements present internal relations adjusted to external 
relations, yet the continuous adjustment of relations can 
scarcely be held to include a Jixed adjustment already made. 
Clearly, life, which is made up of dynamical phenomena, 
cannot be defined in terms that shall at the same time define 
the apparatus manifesting it, which presents only statical 
phenomena. But while this antithesis serves to remind us 
that the fundamental distinction between the organism and 

*^Iii further elucidation of this general doctrine, see First Frineipletf § 25. 


its actions, is as wide as that between Matter and Motion, it 
at the same time draws attention to the fact, that if the 
Btruotnral arrangements of the adult are not properly in- 
cluded in the definition, yet the developmental processes by 
which those arrangements were established, are included. 
For that process of evolution during which the organs of the 
embryo are fitted to their prospective functions, is from be- 
ginning to end the gradual or continuous adjustment of in- 
ternal relations to external relations. Moreover, those struc- 
tural modifications of the adult organism, which, imder change 
of climate, change of occupation, change of food, slowly bring 
about some re-arrangement in the orgauio balance, must simi- 
larly be regarded as continuous adjustments of internal re- 
lations to external relations. So that not only does the de- 
finition, as thus expressed, comprehend all those activities, 
bodily and mental, which constitute our ordinary idea of Life; 
but it also comprehends, both those processes of development 
by which the organism is brought into general fitness for 
these activities, and those after-processes of adaptation by 
which it is specially fitted to its special activities. 

Nevertheless, superior as it is in simplicity and comprehen- 
siveness, so abstract a formula as this is scarcely fitted for 
our present purpose. Reserving its terms for such use as oc- 
casion may dictate, it will be best commonly to employ its 
more concrete equivalent — to consider the internal relations 
as ^'definite combinations of simultaneous and successive 
changes ; '' the external relations as " co-existences and se- 
quences;" and the connexion between them as a "corre- 



§ 31. Alkeady it has been shown respecting each other 
qualification included in the foregoing definition, that the life 
is high in proportion as that qualification is well fulfilled ; 
and it is now to be remarked, that the same thing is especially 
true respecting this last qualification — ^the correspondence be- 
tween internal and external relations. It is manifest d priori, 
that since changes in the physical state of the environment, as 
also those mechanical actions and those yariations of available 
food which occur in it, are liable to stop the processes going 
on in the organism ; and since the adaptive changes in the 
organism have the effects of directly or indirectly counter- 
balancing these changes in the environment ; it follows that 
the life of the organism will be short or long, low or high, 
according to the extent to which changes in the environment 
are met by corresponding changes in the organism. Allow- 
ing a margin for perturbations, the life will continue only 
while the correspondence continues ; the completeness of the 
life will be proportionate to the completeness of the corre- 
spondence ; and the life wiU be perfect only when the corre- 
spondence is perfect. Not to dwell in general statements, 
however, let us contemplate this truth under its concrete 

§ 32. In life of the lowest order, we find that only the 


most prevalent copxistences and sequences in the environ- 
ment, have any simultaneous and successive changes answer- 
ing to them in the organism. A plant's vital processes 
display adjustment solely to the continuous coexistence of 
certain elements and forces surrounding its roots and leaves ; 
and vary only with the variations produced in these ele- 
ments and forces by the sun — are unaffected by the coimtless 
mechanical and other changes occurring aroxmd ; save when 
accidentally arrested by these. The life of a worm is made 
up of actions referring almost exclusively to the tangible pro- 
perties of adjacent things. All those visible and audible 
changes which happen near it, and are connected with other 
changes that may presently destroy it, pass unrecognized-— 
produce in it no adapted changes : its only adjustment of in- 
ternal relations to external relations of this order, is seen 
when it escapes to the surface on feeling the vibrations pro- 
duced by an approaching mole. Adjusted as are the pro- 
ceedings of a bird, to a far greater number of coexistences and 
sequences in the environment, cognizable by sight, hearing, 
scent, and their combinations; and numerous as are the 
dangers it shims and the needs it fulfils, in virtue of this ex- 
tensive correspondence ; it exhibits no such actions as those 
by which a human being counterbalances variations in tem- 
perature and supply of food, consequent on the seasons. And 
when we see the plant eaten, the worm trodden on, the bird 
dead from starvation ; we see alike that the death is an arrest 
of such correspondence as existed; that it occurred when 
there was some change in the environment to which the or- 
ganism made no answering change ; and that thus, both in 
shortness and simplicity, the life was incomplete in propor- 
tion as the correspondence was incomplete. Progress towards 
more prolonged and higher life, evidently implies an ability 
to respond to less general coexistences and sequences. Each 
step upwards must consist in adding to the previously-adjusted 
relations which the organism exhibits, some further relation 

parallel to a further relation in the envircmment. . And the 

6 • 


greater correspondence thus established^ must, other things 
equal, show itself both in greater complexity of life, and 
greater length of life— a truth which will be duly realized on 
remembering that enormous mortality which prevails among 
lowly-organized creatures, and that gradual increase of 
longevity and diminution of fertility which we meet with on 
ascending to creatures of higher and higher development. 

It must, however, be remarked, that while length and com- 
plexity of life are, to a great extent, associated — ^while a 
more extended correspondence in the successive changes, 
commonly implies increased correspondence in the simul- 
taneous changes ; yet it is not uniformly so. Between the 
two great divisions of life — animal and vegetal — ^this contrast 
by no means holds. A tree may live a thousand years, 
though the simultaneous changes going on in it answer only 
to the few chemical affinities in the air and the earth, and 
though its serial changes answer only to those of day and 
night, of the weather and the seasons. A tortoise, which 
exhibits in a given time nothing like the number of internal 
actions adjusted to external ones, that are exhibited by a dog, 
yet lives far longer. The tree by its massive trunk, and the 
tortoise by its hard carapace, are saved the necessity of re- 
sponding to those many surrounding mechanical actions which 
organisms not thus protected must respond to or die; or 
rather — the tree and the tortoise display in their structures, 
certain simple statical relations adapted to meet countless 
dynamical relations external to them. But notwithstanding 
the qualifications suggested by such cases, it needs but to 
compare a microscopic fungus with an oak, an animalcule 
with a shark, a mouse with a man, to recognize the fact that 
this increasing correspondence of its changes with those of 
the environment, which characterizes progressing life, ha- 
bitually shows itself at the same time in continuity and in 

Even were not the connexion between length of life and 
complexity of life thus conspicuous^ it would still be true 


that the degree of life varies with the degree of correspond- 
ence. For if the lengthened existence of a tree be looked 
upon as tantamount to a considerable degree of life ; then it 
must be admitted that its lengthened display of correspond- 
ences is tantamount to a considerable degree of correspond- 
ence. If otherwise it be held, that notwithstanding its much 
shorter existence, a dog must rank above a tortoise in degree 
of life, because of its superior activity ; then it is implied that 
its life is higher, because its simultaneous and successive 
changes are more complex and more rapid — ^because the 
correspondence is greater. And since we regard as the high- 
est life, that which, like our own, shows great complexity in 
the correspondences, great rapidity in the succession of them, 
and great length in the series of them ; the equivalence 
between degree of life and degree of correspondence, is un- 

§ 33. In further elucidation of this general truth, and 
especially in explanation of the irregularities just referred to, 
it requires to be observed, that as the life becomes higher 
the environment itself becomes more complex. Though, 
literally, the environment means all surrounding space with 
the coexistences and sequences contained in it ; yet, practi- 
cally, it often means but a small part of this. The environ- 
ment of an entozoon, can scarcely be said to extend beyond 
the body of the animal in which the entozoon lives. That of 
a fresh-water alga is, virtually, limited to the ditch inhab- 
ited by the alga. And imderstanding the term in this re- 
stricted sense, we shall see that the superior organisms 
inhabit the more complicated environments. 

Thus, contrasted with that found on land, the lower life is 
that found in the sea ; and it has the simpler environment. 
Marine creatures are affected by a smaller number of co- 
existences and sequences than terrestrial ones. Being very 
nearly of the same specific gravity as the surrounding 
medium, they have to contend with less various mechanical 


actions. The zoophyte rooted to a Btone, and the acalephe 
passively borne along in the current, need to undergo no 
internal changes such as those by which the caterpillar meets 
the varying effects of gravitation, while creeping over and 
under the leaves. Again, the sea is liable to none 

of those extreme and rapid alterations of temperature which 
the air suffers. Night and day produce no appreciable 
modifications in it ; and it is comparatively little affected by 
the seasons. Thus its contained feiuna show no marked cor- 
respondences similar to those by which air-breathing crea- 
tures ooimterbalance thermal changes. Further, in. 
respect to the supply of nutriment the conditions are more 
simple. The lower tribes of animals inhabiting the water, 
like the plants inhabiting the air, have their food brought to 
them. The same current which brings oxygen to the oyster, 
also brings it the microscopic organisms on which it 
lives : the disintegrating matter and the matter to be inte- 
grated, coexist under the simplest relation* It is otherwise 
with land animals. The oxygen is everywhere; but that 
which is needed to neutralize its action is not everywhere : it 
has to be sought ; and the conditions under which it is to be 
obtained are more or less complex. So too with 
that liquid by the agency of which the vital processes are 
. carried on. To marine creatures, water is ever present, and by 
the lowest is passively absorbed ; but to most creatures living 
on the earth and in the air, it is made available only through 
those nervous changes constituting perception, and those 
muscular ones by which drinking is effected. Simi- 
larly, the contrast might be continued with respect to the 
electric and hygrometric variations ; and the greater multi- 
plicity of optical and acoustic phenomena with which ter- 
restrial life is surrounded. And tracing upwards from the 
amphibia the widening extent and complexity which the 
environment, as practically considered, assumes — observing 
further how increasing heterogeneity in the flora and fauna 
of the globe, itself progressively complicates the environment 


of each species of organism — it might finally be shown that 
the same general truth is displayed in the history of mankind : 
whose advance in civilization has been simultaneous with 
their advance from the less varied requirements of the torrid 
zone to the more varied requirements of the temperate zone ; 
whose chief steps have been made in regions presenting a 
complicated physical geography ; and who, in the course of 
their progress, have been adding to their physical environ- 
ment a social environment that has been growing even more 
involved. Thus, speaking generally, it is clear that those re- 
lations in the environment to which relations in the organism 
must correspond, themselves increase in number and intricacy 
as the life assumes a higher form. 

§ 34. To make yet more manifest the fact, that the degree 
of life varies as the degree of correspondence, I may here 
point out, that those other distinctions successively noted 
when contrasting vital changes with non- vital changes, are 
aU implied in this last distinction — their correspondence 
with external coexistences and sequences. And to this may 
be added the supplementary fact, that the increasing fulfil- 
ment of those other distinctions which we found to accompany 
increasing life, is involved in the increasing fulfilment of this 
last distinction. To descend to particulars : — We saw- that 
living organisms are characterized by successive changes ; 
and that as the life becomes higher, the successive changes 
become more numerous. Well, the environment is full of 
successive changes, both positive and relative; and the 
greater the correspondence, the greater the number of suc- 
cessive changes an organism must display. We saw that life 
presents simultaneous changes ; and that the more elevated 
it is, the more marked the multiplicity of them. Well, 
besides countless phenomena of coexistence in the environ- 
ment, there are often many changes occurring in it at the 
same moment ; and hence increased correspondence with it, 
supposes an increased display of simultaneous changes in the 


organism. Similarly with the heterogeneity of the changes. 
In the environment the relations are very varied in their 
kinds ; and hence^ as the organic actions come more and more 
into correspondence with them, they also must become very 
varied in their kinds. So again is it, even with definiteness 
of combination. For though the inorganic bodies of which 
the environment mainly consists, do not present definitely- 
combined changes, yet they present definitely-combined 
properties ; and though the minor meteorologic variations of 
the environment, do not show much definitenessof combination, 
yet those resulting from day and night and the seasons do. 
Add to which, that as the environment of each organism 
comprehends all those other organisms existing within its 
sphere of life — as the most important and most numerous 
surrounding changes with which each animal has to deal, 
are the definitely-combined changes exhibited by other 
animals, whether prey or enemies ; it results that definiteness 
of combination is a general characteristic of the external 
changes with which internal ones have to correspond. Hence, 
increase of correspondence involves increased definiteness of 
combination. So that throughout, the correspondence of 
the internal relations with the external ones, is the essential 
thing; and all the special characteristics of the internal 
relations, are but the collateral results of this correspondence. 

§ 35. As affording the simplest and most conclusive proof 
that the degree of life varies as the degree of correspondence, 
it remains to point out that perfect correspondence would be 
perfect life. Were there no changes in the environment but 
such as the organism had adapted changes to meet ; and were 
it never to fail in the efficiency with which it met them ; there 
would be eternal existence and universal knowledge. Death 
by natural decay, occurs because in old age the relations be- 
tween assimilation, oxidation, and genesis of force going on 
in the organism, gradually fall out of correspondence with the 
relations between oxygen and food and absorption of heat by 


the environment. Death from disease, arises either when the 
organism is congenitally defective in its power to balance the 
ordinary external actions by the ordinary internal actions, or 
when there has taken place some unusual external action to 
which there was no answering internal action. Death by 
accident, implies some neighbouring mechanical changes of 
which the causes are either imobserved from inattention, or 
are so intricate that their results cannot be foreseen ; and 
consequently certain relations in the organism are not adjusted 
to the relations in the environment. Manifestly, if, to every 
outer coexistence and sequence by which it was ever in any 
degree affected, the organism presented an answering process 
or act ; the simultaneous changes would be indefinitely nu- 
merous and complex, and the successive ones endless — ^the 
correspondence would be the greatest conceivable, and the 
life the highest conceivable, both in degree and in length. 

§ 36. Before closing the chapter, it will be useful to 
compare the definition of Life here set forth, with the defini- 
tion of Evolution set forth in First Principles. Living 
bodies being bodies which display in the highest degree the 
structural changes constituting Evolution; and Life being 
made up of the functional changes that accompany these 
structural changes ; we ought to find a certain harmony 
between the definitions of Evolution and of Life. Such a 
harmony is not wanting. 

The first distinction we noted between the kind of change 
shown in Life, and other kinds of change, was its serial 
character : we saw that vital change is substantially unlike 
non-vital change, in being made up of successive changes. 
Now since organic bodies display in so much higher a de- 
gree than inorganic bodies, those continuous differentiations 
and integrations which constitute Evolution ; and since the 
re-distributions of matter thus carried so far in a compara- 
tively short period, imply concomitant re-distributions of mo- 
tion ; it is clear that in a given time, organic bodies must 


undergo clianges so comparatiTely numerous as to render the 
fiuccessiveness of their changes a marked characteristic. And 
it will follow d priori, as we found it to do ^ posteriori, that 
the organisms exhihiting Evolution in the highest degree, 
exhihit the longest or the most rapid successions of changes, 
or both. Again, it was shown that vital change is 

distinguished from non- vital change by being made up of 
many simultaneous changes ; and also that creatures possess- 
ing high vitality are marked off from those possessing low 
vitality, by the far greater number of their simultaneous 
changes. Here too there is entire congruity. In First 
Principles, § 116, we reached the conclusion, that a force 
falling on any aggregate is divided into several forces ; that 
when the aggregate consists of parts that are unlike, each 
part becomes a centre of unlike differentiations of the inci- 
dent force ; and that thus the multiplicity of such differen- 
tiations must increase with the multiplicity of the unlike 
parts. It follows necessarily, therefore, that organic aggre- 
gates, which as a class are distinguished from inorganic 
aggregates by the greater number of their unlike parts, must 
be also distinguished from them by the greater number of 
simultaneous changes they display ; and further that the 
higher organic aggregates, having more numerous unlike 
parts than the lower, must undergo more nimierous simxd- 
taneous changes. We next found that the changes 

occurring in living bodies, are contrasted with those occurring 
in other bodies, as being much more heterogeneous; and that 
the changes occurring in the superior living bodies, are 
similarly contrasted with those occurring in inferior ones. 
Well, heterogeneity of function is the correlate of hetero- 
geneity of structure ; and heterogeneity of structure is the 
leading distinction between organic and inorganic aggre- 
gates, as well as between the more highly organized and the 
more lowly organized. By reaction, an incident force must 
be rendered multiform in proportion to the multiformity of 
the aggregate on which it falls ; and hence those most mul- 


tiform aggregates which display in the liighest degree the 
pheiiomena of Evolution structurally considered^ must at the 
same time be aggregates which display in the highest de- 
gree the multiform actions which constitute Evolution 
functionally considered. These heterogeneous changes, 

exhibited simultaneously and in succession by a living or- 
ganism, prove, on further inquiry, to be distinguished by 
their combination from certain non-vital changes which 
simidate them. Here, too, the parallelism is maintained. 
It was shown in § 56 of First Principles, that an essential 
characteristic of Evolution is the integration of parts, which 
accompanies their differentiation — an integration that is 
shown both in the consolidation of each part, and in the 
consolidation of all the parts into a whole. Now, manifestly, 
combination among the changes going on in different com- 
bined parts, must be proportionate to the degree of com- 
bination among these parts : the more mutually-dependent 
the parts, the more mutually-dependent must be their 
actions. Hence, animate bodies having greater co-ordin- 
ation of parts than inanimate ones, must exhibit greater 
co-ordination of changes. And this greater co-ordination of 
their changes must not only distinguish organic from inor- 
ganic aggregates ; but must, for the same reason, distinguish 
higher organisms from lower ones, as we found that it 
did. Tet once more, it was pointed out that the 

changes constituting Life, differ from other changes in the 
definitetiess of their combination ; and that a distinction like in 
kind, though less in degree, holds between the vital changes 
of superior creatures and those of inferior creatures. These, 
also, are contrasts in harmony with the contrasts disclosed by 
the analysis of Evolution. We saw (First Principles, §§ 54, 
55) that during Evolution, there is an increase of definiteness 
as well as an increase of heterogeneity. We saw that the 
integration accompanying differentiation, has necessarily the 
effect of increasing the distinctness with which the parts are 
marked off from each other ; and that so, out of the inco- 


herent and indefinite, there arises the coherent and definite. 
But a coherent whole made up of definite parts definitely 
combined, must exhibit more definitely combined changes 
than a whole made up of parts that are neither definite in 
themselves nor in their combination. Hence, if living bodies 
display more than other bodies this structural definiteness, 
then, definiteness of combination must be a characteristic of 
the changes constituting Life ; and must also distinguish the 
vital changes of higher organisms from those of lower organ- 
isms. Finally, however, we discovered that all these 
peculiarities are subordinate to the one fundamental pecu- 
liarity, that vital changes take place in correspondence with 
external co-existences and sequences ; and that the highest 
possible Life is reached, when there is some inner relation of 
actions fitted to meet every outer relation of actions by 
which the organism can be affected. But this conception of 
the highest possible Life, is in perfect harmony with the con- 
ception, before arrived at, of the ultimate limit of Evolution. 
When treating of equilibration as exhibited in organic 
phenomena {First Principles, §§ 133, 134), it was pointed 
out, that the continual tendency is towards the establishment 
of a balance between inner and outer changes. It was 
shown that '' the final structural arrangements must be such 
as will meet all the forces acting on the aggregate, by 
equivalent antagonistic forces,'^ and that " the maintenance 
of such a moving equilibrium '^ as an organism displays, 
*' requires the habitual genesis of internal forces correspond- 
ing in number, directions, and amoimts, to the external 
incident forces — ^as many inner functions, single or com- 
bined, as there are single or combined outer actions to be 
met.'' It was shown, too, that the relations among concep- 
tions and ideas, are ever in progress towards a better balance 
between mental actions and those actions in the environment 
to which conduct must be adjusted. So that that main- 
tenance of a correspondence between inner and outer rela- 
tions, which we have here found to constitute Life, and the 


perfection of which is the perfection of Life, answers com- 
pletely to that state of organic moving equilibrium which 
we saw arises in the course of Evolution, and tends ever to 
become more complete. 

There is much significance in this complete parallelism. 
That two inquiries starting from different points and carried 
on in different ways, should lead to conclusions so entirely 
harmonizing with each other, cannot fail further to confirm 
these conclusions ; if further confirmation of them be needed. 



§ 37. Wb are now in a position to map-out the boundaries 
and divisions of our subject. Grouping together the general 
results arrived at in the first three chapters, and joining with 
them the results which the last three chapters have brought us 
to, we shall be prepared to comprehend the science of Biology 
as a whole ; and to see how its truths may best be classified. 

In the chapters treating of Organic Matter, the Actions of 
Forces on it, and its Reactions on Forces, the generalizations 
reached were these : — that organic matter is specially sensi- 
tive to surroimding agencies; that in consequence of the 
extreme instability of the compounds it contains, minute dis- 
turbances can cause in it large amounts of re-distribution ; 
and that during the fall of its unstably-arranged atoms into 
stable arrangements, there are given out proportionately 
large amounts of motion. We saw that organic matter is so 
constituted, that small incident actions are capable of initiat- 
ing great reactions — setting up extensive structural modifica- 
tions, and liberating large quantities of power. In 
the chapters just concluded, the changes of which life is 
made up, were shown to be so adjusted as to balance outer 
changes. And the general process of the adjustment we 
found resolves itself into this ; that if in the environment 
there are any related actions, A and B, by which the or- 


ganism is affected, then if A produces in the organism some 
change a, there follows in the organism some change b, fitted 
in time, direction, and amount to meet the action B — a 
change which is often required to be much larger than its 
antecedent. Mark, now, the relation between these 

two final results. • On the one hand, for the maintenance of 
that correspondence between inner and outer actions which 
constitutes Life, an organism must be susceptible to small 
changes from small external forces (as in sensation), and must 
be able to initiate large changes in opposition to large external 
forces (as in muscular action). On the other hand, organic 
matter is at once extremely sensitive to disturbing agencies 
of all kinds, and is capable of suddenly evolving motion in 
great amounts. That is to say, the constitution of organic 
matter specially adapts it to receive and produce the internal 
changes required to balance external changes. 

This being the general character of the vital Functions, 
and of the Matter in which they are performed, the science 
of Biology becomes an account of all the phenomena attend* 
ant on the performance of such Functions by such Matter— 
an account of all the conditions, concomitants, and conse- 
quences, under the various circumstances fallen into by living 
bodies. If all the functional phenomena which living bodies 
present, are, as we have concluded, incidents in the main- 
tenance of a correspondence between inner and outer ac- 
tions ; and if all the structural phenomena which living 
bodies present, are direct or indirect concomitants of func- 
tional phenomena ; then the entire Science of Life, must con- 
sist in a detailed interpretation of all these functional and 
structural phenomena in their relations to the phenomena of 
the environment. Immediately or mediately, proximately 
or remotely, every trait exhibited by organic bodies, as 
distinguished from inorganic bodies, must be referable to 
this continuous adjustment between their actions and the 
actions going on around them. Such being the extent and 
nature of our subject-matter, it may be thus divided. 


1. An account of the structural phenomena presented by 
organisms. And this subdivides into : — 

a. The structural phenomena presented by individual 

b. The structural phenomena presented by successions 
of organisms. 

2. An account of the fiinctional phenomena which or- 
ganisms present. And this, too, admits of sub-division into : — 

a. The functional phenomena of individual organisms. 

b. The functional phenomena of successions of organisms. 

3. An account of the actions of Structure on Fimction, 
and the re-actions of Function on Structure. And like the 
others, this is divisible into : — 

a. The actions and re-actions as exhibited in individual 

b. The actions and re-actions as exhibited in successions 
of organisms. 

4. An account of the phenomena attending the production 
of successions of organisms : in other words — the phenomena 
of Genesis. 

There is, indeed, another mode of grouping the facts of 
Biology, with which all are familiar. According as they 
are facts of animal or vegetal life, they may be classed 
under the heads of Zoology and Botany. But this di- 
vision, though convenient and indeed necessary for practi- 
cal purposes, is one that does not here concern us. Dealing 
with organic structures and functions in connexion with 
their causes, conditions, concomitants, and consequences, 
Biology cannot divide itself into Animal-Biology and Vege- 
tal-Biology; since the same fundamental classes of phe- 
nomena are common to both. Becognizing this familiar 
distinction only as much as convenience obliges us to do, let 
us now pass on to consider, more in detail, the classification 
of biologic phenomena, above set down in its leading outlines. 

§ 38. The facts of structure which an individual or- 


ganism exhibits, are of two cliief kinds. In order of con- 
spiouousnesSy though not in order of time, there come first 
those ultimate arrangements of parts which characterize the 
organism in its mature state — an account of which, commonly 
called Anatomy, is more properly called Morphology. And 
second, there come those successive modifications through 
which the organism passes in its deyeloinnent from the germ 
to the adult form — an account of which is called Embryology. 

The facts of structure which any succession of inc^yidual 
organisms exhibits, admit of similar classification. On the 
one hand, we have those inner and outer difierences of shape, 
that are liable to arise between the adult members of suc« 
cessiye generations descended from a common stock — differ- 
ences which, though usually not marked between adjacent 
generations, may in course of many generations become great. 
And on the other hand, we have those developmental modi- 
fications through which such modifications of the descended 
forms are reached. 

The interpretation of structure, as exhibited in individual 
organisms and successions of organisms, is aided by two sub- 
sidiary divisions of biologic inquiry, named Comparative 
Anatomy (properly Comparative Morphology) and Compara- 
tive Embryology. These cannot properly be regarded as in 
themselves parts of Biology ; since the facts embraced under 
them are not substantive phenomena, but are simply inci- 
dental to substantive phenomena. All the facts of structural 
Biology are comprehended under the two foregoing sub- 
divisions; and the comparison of these facts as presented 
in different classes of organisms, is simply a method of inter- 
preting the real relations and dependencies of the facts 

Nevertheless, though Comparative Morphology and Com- 
parative Embryology do not disclose additional series of con- 
crete or q)ecial facts, they lead to the establishment of certain 
abstract or general facts. By them it is made manifest that 
underneath the supei'ficial difierences of groups and classes 


and types of organisms, there are hidden fundamental simi- 
larities ; and that the courses of development in such groups 
and classes and types, though iu many respects divergent, 
are in some essential respects, coincident. The wide truths 
thus disclosed, come imder the heads of General Morphology 
and General Emhryology. 

By contrasting the structures of organisms, there is also 
achieved that grouping of the like and separation of the 
unlike, called Classification. First by observation of ex- 
ternal characters ; second by observation of internal charac- 
ters ; and third by observation of the phases of development ; 
it is ascertained what organisms are most similar in all 
particulars ; what organisms are like each other in every 
important attribute ; what organisms have common primor-' 
dial characters. Whence there finally results such an ar- 
rangement of organisms, that if certain structural attributes 
of any one be given, its other structural attributes may be 
empirically predicted ; and which preparer the way for that 
interpretation of their relations and genesis, which forms an 
important part of rational Biology. 

§ 39. The second main division of Biology, above de- 
scribed as embracing the functional phenomena of organisms, 
is that which is in part signified by Physiology : the remain- 
der being what we distinguish as Psychology. Both of 
these fall into subdivisions that may best be treated separ- 
ately. That part of Physiology which is concerned 
with the molecular changes going on in organisms, is known 
as Organic Chemistry. An account of the modes in which the 
force generated in organisms by chemical change, is trans- 
formed into other forces, and made to work the various or- 
gans that carry on the functions of Life, comes imder the 
head of Organic Physics. Psychology, which is 
mainly concerned with the adjustment of vital actions to 
actions in the environment (in contrast with Phpiology, 
which is mainly concerned with vital actions apart from 


actions in tlie environment) consists of two quite distinct por- 
tions. Objective Psychology deals with those functions of the 
nervo-muscular apparatus by which such organisms as possess 
it, are enabled to adjust inner to outer relations ; and includes 
also, the study of the same functions as externally manifested 
in conduct. Subjective Psychology deals with the sensations, 
perceptions, ideas, emotions, and volitions that are the direct 
or indirect concomitants of this visible adjustment of inner to 
outer relations — considers these several kinds of conscious- 
ness in their genesis, and their connexions of co-existenoe and 
succession. Consciousness under its different modes and 
forms, being a subject-matter radically distinct in nature from 
the subject-matter of Biology in general ; and the method of 
self-analysis, by which alone the laws of dependence among 
changes of consciousness can be found, being a method un- 
paralleled by anything in the rest of Biology ; we are 
obliged to regard Subjective Psychology as a separate study 
—not absolutely, of course, but relatively to the mind of each 
student. And since it would be very inconvenient to dis- 
sociate Objective Psychology from Subjective Psychology, we 
are practically compelled to deal with the two as forming an 
independent sub-science, to be treated apart from the lower 
divisions of Biology. 

Obviously, the functional phenomena presented in succes- 
sions of organisms, similarly divide into physiological and 
psychological. Under the physiological, come the 

modifications of bodily actions that arise in the course of 
generations, as concomitants of structural modifications ; and 
these may be modifications, qualitative or quantitative, in 
the molecular changes classed as chemical, or in the organic 
actions classed as physical, or in both. Under the 

psychological, come the qualitative and quantitative modifica- 
tions of instincts, feelings, conceptions, and mental changes 
in general, that occur in creatures having more or less 
intelligence, when certain of their conditions are changed. 
This, like the preceding department of Psychology, has in 


the abstract two different aspects — the objectiye and the sub- 
jective. Practically, however, the objective, which deals 
with these mental modifications as exhibited in the changing 
habits and abilities of successive generations of creatures, is 
the only one that admits of scientific investigation ; since the 
corresponding alterations in consciousness, cannot be im- 
mediately known to any but the subjects of them. Evidently^ 
convenience requires us to class this part of Psychology along 
with the other parts, in a distinct sub-science. 

Light is thrown on functions, as weU as on structures, 
by comparing organisms of different kinds. Comparative 
Physiology and Comparative Psychology, are the names 
given to those collections of facts respecting the homologies 
and analogies, bodily and mental, that are brought to light by 
this kind of inquiry. These classified observations concern- 
ing likenesses and differences of functions, are helpers to 
interpret functions in their essential natures and relations. 
Hence Comparative Physiology and Comparative Psychology 
are names of methods, rather than names of true subdivisions 
of Biology. 

Here, however, as before, the comparison of special truths, 
besides fiusilitating their interpretation, brings to light certain 
general truths. Contrasting bodily and mental functions as 
exhibited in various orders of organisms, shows that there 
exists, more or less extensively, a community of. processes 
and methods. Hence result two groups of abstract proposi- 
tions, constituting General Physiology and General Psy- 

§ 40. In these various divisions and sub-divisions of the 
first two great departments of Biology, the phenomena of 
Structure are considered separately from the phenomena of 
Fimction, so far as separate treatment of them is possible. 
The third great department of Biology deals with them in 
their necessary connexions. It comprehends the determin- 


ation of functions by structures, and the determination of 
structures by functions. 

As displayed in individual organisms, the action of struc- 
tures on functions is to be studied, not only in the broad and 
familiar fact that the general kind of life an organism leads 
is necessitated by the main characters of its organization, 
but in the more special and less conspicuous fact, that between 
members of the same species, minor differences of structure lead 
to minor differenoesof power to perform certain kindsof action, 
and of tendency to perform such kinds of action. Con- 

versely, under the re-actions of function on structure as 
displayed in individual organisms, come the facts showing 
that functions, when ful&Ued to their normal extents, main- 
tain integrity of structure in their respective organs ; and 
that within certain limits, the increase of functions is followed 
by such structural changes in their respective organs, as 
enables the organs to discharge better their extra Amotions. 

Inquiry into the action of structure on Amotion as dis- 
played in successions of organisms, introduces us to such 
phenomena as Mr Darwin's ''Origin of Species" deals with. 
In this category come all proofs of the general truth, that 
when an individual is enabled by a certain structural pecu** 
liarity, to perform better than others of its species some 
advantageous action ; and when it bequeaths more or less of 
its structural peculiarity to descendants, among whom those 
which have it most markedly, are best able to thrive and 
propagate ; there arises through this continuous action of 
structure on function, a visibly modified type of structure, 
having a more or less distinct function. In the cor- 

relative class of facts, which come under the category of re- 
actions of function on structure as exhibited in successions of 
organisms, are to be placed all those modifications of struc- 
ture which arise in races, when changes of conditions entail 
changes in the balance of their fimctions. Here is to be 
studied the way in which altered function externally necessi- 


tated, works, by re-action, altered structure ; and howinsucceed- 
ing generations, this altered structure may be made continu- 
ally more marked by this altered fimction. Thougb 
logically distinct, these two sub-divisions of biologic inquiry 
cannot in practice be carried on apart. A speciality of struc- 
ture which leads to an excess of function in any direction, 
is, by the perpetual re-action of function, rendered ever more 
decided. A speciality of function, by calling forth a corre- 
sponding speciality of structure, produces an increasingly 
efficient discharge of such function. Whichever of the two 
initiates the change, there goes on between them an unceas- 
ing action and re-action, producing in them co-ordinate 

§ 41. The fourth great division of Biology, comprehend- 
ing the phenomena of Genesis, may be conveniently separated 
into three sub-divisions. 

Under the first, comes a description of all the special 
modes whereby the multiplication of organisms is carried on; 
which modes range themselves under the two chief heads of 
sexual and asexual. An accoimt of Sexual Multiplication in- 
cludes the various methods by which germs and ova are 
fertilized, and by which, after fertilization, they are furnished 
with the materials, and maintained in the conditions, needful 
for their development. An account of Asexual Multiplica- 
tion includes the various methods by which, from the same 
fertilized germ or ovum, there are produced many organisms 
that are partially or totally independent of each other. 

The second of these sub-divisions deals with the phenomena 
of Genesis in the abstract. It takes for its subject-matter, such 
general questions as — What is the end subserved by the 
union of sperm-cell and germ-cell f Why cannot all multi- 
plication be carried on after the asexual method? What 
are the laws of hereditary transmission? What are the 
causes of variation ? 

The third sub-division is devoted to still more abstract 


aspects of the phenomena. Keeognizing the general facts of 
multiplication, without reference to their modes or immediate 
causes, it concerns itself simply with the different rates of 
multiplication in different kinds of organisms, and different 
individuals of the same kind. Generalizing the numerous 
contrasts and variations of fertility, it seeks a rationale of 
them in their relations to other organic phenomena. 

§ 42. Such appears to be the natural arrangement of 
divisions and sub-divisions which Biology presents, when re- 
garded from the highest point of view, as the Science of 
Life — the science which has for its subject-matter, the cor- 
respondence of organic relations, with the relations amid 
which organisms exist. This, however, is a classification of 
the parts of Biology when fully developed ; rather than a 
classification of the parts of Biology as it now stands. 
Several of the sub-divisions above named have no recognized 
existence ; and sundry of the others are in quite rudimentar}^ 
states. It is therefore impossible now to fill in, even in the 
roughest way, more than a part of the outlines here 

Our course of inquiry being thus in great measure de- 
termined by the present state of knowledge, we are com- 
pelled to follow an order widely different from this ideal one. 
It will be necessary first to give an account of those empiri- 
cal generalizations which naturalists and physiologists have 
established : arranging them rather with a view to facility 
of comprehension than to logical sequence ; and append- 
ing to those which admit of it, such deductive interpreta- 
tions as First Principles furnish us with. Having done this, 
we shall be the better prepared for dealing with the lead- 
ing truths of Biology, in connexion with the doctrine of 




§ 43. Perhaps the widest and most familiar induction of 
Biology, is that organisms grow. While, however, this is a 
characteristic so habitually and markedly displayed by plants 
and animals, as to be carelessly thought peculiar to them, 
it is really not so. Under appropriate conditions, increase of 
size takes place in inorganic aggregates, as well as in organic 
aggregates. Crystals grow ; and often far more rapidly than 
living bodies. Where the requisite materials are supplied in 
the requisite forms, growth may be witnessed in non-crystal- 
line masses: instance the fungus-like accumulation of 
carbon that takes place on the wick of an unsnuffed candle. 
On an immensely larger scale, we have growth in geologic 
formations : the slow accumulation of deposited sediment into 
a stratum, is not distinguishable from growth in its widest 
acceptation. And if we go back to the genesis of celestial 
bodies, assuming them to have arisen by Evolution, these, 
too, must have gradually passed into their concrete shapes 
through processes of growth. Growth is indeed a concomi- 
tant of Evolution ; and if Evolution of one kind or other is 
universal, growth is universal—universal, that is, in the 
sense that all aggregates display it in 9ome way at some 

The essential community of nature between organic 
growth and inorganic growth, is, however, most clearly seen 


on observing that they \>Qth result in the same way. The 
segregation of different kinds of detritus from each other, as 
well as from the water carrying them, and their aggregation 
into distinct strata, is but an instance of a universal tend- 
ency towards the union of like units and the parting of un- 
like units (First Principks, § 123). The deposit of a crystal 
from a solution, is a differentiation of the previously mixed 
atoms ; and an integration of one class of atoms into a solid 
body, and the other class into a liquid solvent. Is not the 
growth of an organism a substantially similar process? 
Around a plant there exist certain elements that are like 
the elements which form its substance ; and its increase of 
size is effected by continually integrating these surrounding 
like elements with itself. Nor does the animal fundament- 
ally differ in this respect from the plant or the crystaL Its 
food is a portion of the environing matter, that contains some 
compound atoms like some of the compoimd atoms constitut- 
ing its tissues; and either through simple imbibition or 
through digestion, the animal eventually integrates with it- 
self, units like those of which it is built up, and leaves behind 
the unlike units. To prevent misconception, it may 

be well to point out that growth, as here defined, must be 
distinguished from certain apparent and real augmentations 
of bulk which simulate it. Thus, the long, white potato- 
shoots thrown out in the dark, are produced at the expense 
of the substances which the tuber contains : they illustrate 
not the accumulation of organic matter, but simply its re* 
arrangement. Certain animal-embryos, again, during their 
early stages, increase considerably in size without assimilating 
any solids from the environment; and they do this by 
absorbing the surrounding water. Even in the highest 
organisms, as in children, there appears sometimes to occur 
a rapid gain in dimensions, that does not truly measure the 
added quantity of organic matter; but is in part due to 
changes analogous to those just named. Alterations of this 

GROWTH. 109 

kind must not be confounded with tliat growth, properly so 
called, of which we have here to treat. 

The next general fact to be noted respecting organic 
growth, is, that it has limits. Here there appears to be a 
distinction between organic and inorganic growth ; but this 
dis(tinction is by no means definite. Though that aggrega- 
tion of inanimate matter which simple attraction produces, 
may go on without end ; yet there appears to be an end to 
that more definite kind of aggregation which results from 
polar attraction. Different elements and compounds, habitu- 
ally form crystals more or less unlike in their sizes ; and each 
seems to have a size that is not usually exceeded without a 
tendency arising to form new crystals rather than to increase 
the old. On looking at the organic kingdom as a 

whole, we see that the limits between which growth ranges, 
are very wide apart. At the one extreme, we have monads 
so minute as to be rendered but imperfectly visible by micro- 
scopes of the highest power ; and at the other extreme, we 
have trees of 300 feet high, and animals of 100 feet long. 
It is true that though in one sense this contrast may be 
legitimately drawn, yet in another sense it may not ; since 
these largest organisms are made by the combination of units 
that are individually like the smallest. A single plant of the 
genus ProtococcuSj is of the same structure as one of the 
many cells imited together to form the thallus of some 
higher Alga, or the leaf of a phsanogam. Each separate 
shoot of a phaanogam is usually the bearer of many 
leaves. And a tree is an assemblage of numerous united 
shoots. One of these great teleophytes is thus an ag- 
gregate of aggregates of aggregates of units, which sever- 
ally resemble protophytes in their sizes and structures; 
and a like building up is traceable throughout a consider- 
able part of the animal kingdom. Even, however, when 
we bear in mind this qualification, and make our com- 
parisons between organisms of the same degree of compo- 


eition, we still find the limit of growth to have a great 
range. The smallest branched flowering plant is extremely 
insignificant by the side of a forest tree ; and there is an 
enormous difference in bulk between the least and ihe great- 
est mammal. But on comparing members of the same 
species, we discover the limit of growth to be much less vari- 
able. Among the Protozoa and Protophytay each kind has a 
tolerably constant adult size ; and among the most complex 
organisms, the differences between those of the same kind 
that have reached maturity, are usually not very great. 
The compound plants do, indeed, sometimes present marked 
contrasts between stunted and well-grown individuals ; but 
the higher animals diverge but inconsiderably from the 
average standards of their species. 

On surveying the facts with a view of empirically general- 
izing the causes of these differences, we are soon made aware 
that by variously combining and conflicting with each other, 
these causes produce great irregularities of result. It be- 
comes manifest that no one of them can be traced to its. 
consequences, unqualified by the rest. Hence the several 
statements contained in the following paragraphs, must be 
taken as subject to mutual modification. 
:. Let us consider first, the connexion between degree of 
growth and complexity of structure. This connexion being 
involved with many others, becomes apparent only on so 
averaging the comparisons, as to eliminate differences among 
the rest. Nor does it hold at all where the conditions are 
radically dissimilar; as between plants and animals. But 
bearing in mind these qualifications, we shall see that 
organization has a determining influence on increase of 
mass. Of plants the lowest, classed as Thallogens, 

usually attain no considerable size. Lichens, Algsd, and Fun- 
gi, count among their numbers but few bulky species : the 
largest, such as certain Algod found in antartic seas, not 
serving greatly to raise the average. Though among 
Acrogens there are some, as the Tree-ferns, which attain a 


considerable height, the majority are but of. humble growth. 
The Endogens, including at one extreme 6mall grasses and 
at the other tall palms, show us an average and a maximum 
greater, than that reached by the Acrogens. And the £n- 
dogens are exceeded by the Exogens; among which are 
found the mpnarchs of the vegetal kingdom. Pass- 

ing to animals, we meet the fact that the size attained by 
Vertebraia is usually much greater than the size attained by 
Invertehrata. Of invertebrate animals the smallest, classed 
as ProtozoUy are also the simplest; and the largest, be- 
longing to the Annuloaa and Mollusca, are among the most 
eomplex of their respective types. Of vertebrate animala 
we see that the greatest are Mammals ; and that though^ 
in past epochs, there were reptiles of vast bulk, their bulk 
did not equal that of the whale. Between reptiles and 
birds, and between land-vertebrates and aquatic vertebrates, 
the relation does not hold : the conditions of existence be- 
ing in these cases widely different. But among fishes as a 
clasSj and among reptiles as a class, it is observable that, 
speaking generally, the larger species are framed on the 
higher types. The critical reader, who has men- 

tally checked these statements in passing them, has doubtless 
already seen that this relation is not a dependence of or- 
ganization on growth, but a dependence of growth on or- 
ganization. The majority of Exogens are smaller than some 
Endogens ; many Endogens are exceeded in size by certain 
Acrogens ; and ev^n among Thallogens, the least developed 
of plants, there are kinds of a size which many plants of the^ 
highest order do not reach. Similarly among animals : 
there are plenty of Crustaceans less than ActinicB ; numerous 
reptiles are smaller than some fish; the majority of mam- 
mals are inferior in bulk to the largest reptiles ; and in the 
contrast between a moujse and a well-grown Medusa, we see a 
creature that is elevated in the scale of organization, ex- 
ceeded in mass by one that is extremely degraded. Clearly 
then, it cannot be held that high organization is habitually- 


i^ompanied by great size. The proposition liere illustrated 
is the converse one, that great size is habitually accompanied 
by high organization. The conspicuous fact that the largest 
species of both animals and vegetals bebng to the highest 
classes; and that throughout their various sub-classes the 
higher usually contain the more bulky forms ; shows this 
connexion as clearly as we can expect it to be shown, amid 
so many modifying causes and conditions. 

The relation between growth and supply of available 
nutriment, is too familiar a relation to need proving. There 
are^ however, some aspects of it that must be contemplated be- 
fore its implications can be fully appreciated. Among 
plants, which are all constantly in contact with the gaseous, 
liquid, and solid matters to be incorporated with their tissues ; 
and which, in the same locality, receive not very unlike 
amounts of light and heat; differences in the supplies of 
available nutriment, have but a subordinate connexion with 
differences of growth. Though in a cluster of herbs spring- 
ing up from the seeds let fall by a parent, the greater size of 
some than of others is doubtless due to better nutrition, 
consequent on accidental advantages ; yet no such inter- 
pretation can be given of the contrast in size between these 
herbs and an adjacent tree. Other conditions here come into 
play : one of the most important probably being, an absence in 
the one case, and presence in the other, of an ability to se- 
crete such a quantity of ligneous fibre as will produce a stem 
capable of supporting a large growth. Among 
animals, however, which (excepting some Entozoa) differ 
from plants in this, that instead of bathing their surfaces, 
the matters they subsist on are dispersed, and have to be 
obtained; the relation between available food and growth, 
is shown with more regularity. The J^roiozoa, living on 
microscopic fragments of organic matter contained in the 
surrounding water, are unable, during their brief lives, to 
accumulate any considerable quantity of nutriment. Polypes 
and MqlluBcoida, having for food these scarcely visible mem- 

GROWTH. 113 

bers of the animal kingdom, are, though large compared 
with their prey, small as measured by other standards : even 
when aggregated into groups of many individuals, which 
severally catch food for the common weal, they are often so 
inconspicuous as readily to be passed over by the unobservant. 
And if from this point upwards we survey the successive 
grades of animals, it becomes manifest that, in proportion as 
the size is great, the masses of nutriment are either large, or, 
what is practically the same thing, are so abundant and so 
grouped as that large quantities may be readily taken in. 
Though, for example, the greatest of mammals, the arctic 
whale, feeds on such comparatively small creatures as the 
acalephes and molluscs floating in the seas it inhabits, its 
method of gulping in whole shoals of them and filtering 
away the accompanying water, enables it to secure great 
quantities of food. We may then with safety say, that, 
other things equal, the growth of an animal depends on the 
abundance and sizes of the masses of nutriment which its 
powers enable it to appropriate. Perhaps it may be 

needful to add that, in interpreting this statement, the 
number of competitors must be taken into account. Clearly, 
not the absolute, but the relative, abundance of fit food is 
the point ; and this relative abundance very much depends 
on how many individuals are competing for the food. Thus 
all who have had experience of fishing in Highland lochs, 
know that where the trout are numerous they are small, and 
that where they are comparatively large they are compara- 
tively few. 

What is the relation between growth and expenditure of 
force? is a question which next presents itself. Though 
there is reason to believe such a relation exists, it is not very 
readily traced : involved as it is with so many other rela- 
tions. Some contrasts, however, may be pointed out, that 
appear to give evidence of it. Passing over the vegetal 
kingdom, throughout which the expenditure of force is too 
small to allow of such a relation being visible ; let us seek in 



the animal kingdom, some case where classes otherwise 
allied, are contrasted in their locomotive activities. Let us 
compare birds on the one hand, with reptiles and mammals 
on the other. It is an accepted doctrine that birds are 
organized on a type closely allied to the reptilian type, but 
superior to it ; and though in many respects the organization 
of birds is inferior to that of mammals, yet in other respects, 
as in the greater heterogeneity and integration of the skeleton, 
the more complex development of the respiratory system, 
and the higher temperature of the blood, it may be held 
that birds stand above mammals. Hence were growth de- 
pendent only on organization, we might infer that the limit 
of growth among birds should not be much short of that 
among mammals ; and that the bird-type should admit of a 
larger growth than the reptile-type. Again, we see no mani- 
fest disadvantages under which birds labour in obtaining 
food, but from which reptiles and mammals are free. On the 
contrary, birds are able to get at food that is fixed beyond 
the reach of reptiles and mammals ; and can catch food that 
is too swift of movement to be ordinarily caught by reptiles 
and mammals. Nevertheless, the limit of growth in birds, 
falls far below that reached by reptiles and mammals. With 
what other contrast between these classes, is this contrast 
connected P May we not suspect that it is connected with 
the contrast between their amounts of locomotive exertion P 
Whereas mammals (excepting bats, which are small), are 
during aU their movements supported by solid surfaces or 
dense liquids ; and whereas reptiles (excepting the ancient 
pterodactyles, which were not very large), are similarly re- 
stricted in their spheres of movement ; the majority of birds 
move more or less habitually through a rare medium, in which 
they cannot support themselves without relatively great 
efforts. The conclusion that there exists this inverse 

ratio between growth and expenditure of force, is enforced 
by the significant fact, that those members of the class Aves, 
as the Dinornis and Epiornis^ which approached in size to 

GROWTH. 115 

the larger Mammalia and Reptilia^ were creatures incapable 
of flight — creatures which did not expend this excess of 
force in locomotion. Further evidence that there is 

an antagonism between the increase of bulk and the quantity 
of motion evolved by an organism, is supplied by the ge- 
neral experience, that human beings and domestic animals, 
when overworked while growing, are prevented from attain- 
ing the ordinary dimensions. 

One other general truth concerning degrees of growth, 
must be set down. It is a inde, having exceptions of no 
great importance, that large organisms commence their 
separate existences as masses of organic matter more or less 
considerable in size, and commonly with organizations more or 
less advanced; and that throughout each organic sub-kingdom, 
there is a certain general, though irregular, relation between 
the initial and the final bulks. Vegetals exhibit this 

relation much less clearly and constantly than animals. Yet 
though, among the plants that begin life as minute spores, 
there are some which, under their special conditions, grow to 
considerable sizes, the immense majority of them remain 
small. While, conversely, the great Endogens and Exogens, 
when thrown off from their parents, have already the formed 
organs of young plants, to which are attached large stores of 
highly nutritive matter. That is to say, where the young 
plant consists merely of a centre of development, the ultimate 
growth is commonly insignificant ; but where the growth 
is to become great, there exists to start with, a well-developed 
embryo and a stock of assimilable matter. Through- 

out the animal kingdom, this relation is tolerably regular. 
Save among classes that escape the ordinary requirements of 
animal life, small germs or eggs do not give rise to bulky 
creatures. Where great bulk is to be reached, the young 
proceeds from an Qgg of considerable bulk, or is born of con- 
siderable bulk ready-organized and partially active. In the 
class fishes, for instance, a certain average proportion obtains 
between the sizes of the ova and the sizes of the adult indi- 

8 ♦ 


dividuals ; and among the highest fishes^ as sharks, the 
eggs are comparatively few and comparatively large. Rep- 
tiles have eggs that are smaller in number, and relatively 
greater in mass, than those of fishes ; and throughout this 
class, too, there is a general ratio between the bulk of the egg 
and the bulk of the adult creature. As a group, birds show 
us a further limitation in the number of their eggs, and a 
further increase in their relative sizes ; and from the minute 
eggs of the humming-bird up to the immense ones of the 
J^iorwM, holding several quarts, we see that, speaking ge- 
nerally, the greater the eggs, the greater the birds. Finally, 
among mammals (omitting the marsupials) the young are 
bom, not only of comparatively large sizes, but with ad- 
vanced organizations; and throughout this sub-division of 
the vertebrata, as throughout the others, there is a mani* 
fest connexion between the sizes at birth and the sizes at 
maturity. As having a kindred meaning, there 

must finally be noted the fact, that the young of these 
highest animals, besides starting in life with bodies of 
considerable sizes, almost fully organized, are, during sub- 
sequent periods of greater or less length, supplied with nutri- 
ment — in birds by feeding, and in mammals by suckling and 
afterwards by feeding. That is to say, beyond the mass and 
organization directly bequeathed, a bird or mammal obtains 
a further large mass at but little cost to itself. 

Were an exhaustive treatment of the topic intended, it 
would be needful to give a paragraph to each of the many 
incidental circumstances by which growth may be aided or 
restricted. Such facts as that an entozoon is limited by the 
size of the creature, or even the organ, in which it thrives ; 
that an epizoon, though getting abundant nutriment with- 
out appreciable exertion, is restricted to that small bulk at 
which it escapes ready detection by the animal it infests ; 
that sometimes, as in the weazel, smallness is a condition to 
successM pursuit of the animals preyed upon ; and that at 
other times, the advantage of resembling certain other crea- 

GROWTH. 1 17 

tures, and so deceiving enemies or prey, becomes an indirect 
cause of restricted size. But the present purpose is simply 
to set down those most general relations between growth and 
other organic phenomena, which induction leads us to. 
Having done this, let us go on to inquire whether these 
general relations can be deductively established. 

§ 44. That there must exist a certain dependence of 
growth on organization, may be shown d priori. When we 
consider the phenomena of Life, either by themselves or in 
their relations to surrounding phenomena, we see that, other 
things equal, the larger the aggregate the greater is the 
needftd complexity of structure. 

In plants, even of the highest type, there is a com- 
paratively small mutual dependence of parts : a gathered 
flower-bud will unfold and flourish for days, if its istem be 
immersed in water ; and a shoot cut off from its parent-tree 
and stuck in the ground, will grow. The respective parts 
having vital activities that are not widely unlike, it is pos- 
sible for great bulk to be reached without that structural 
complexity required for combining the actions of parts. 
Even here, however, we see that for the attainment of great 
bulk, there requires such a degree of organization as shall 
co-ordinate the functions of roots and branches — we see 
that such a size as is reached by trees, is not possible 
without an efficient vascular system enabling the remote 
organs to utilize each other's products. And we see that 
such a co-existence of large growth with low organization, 
as occurs in some of the marine Algce, occurs where the 
conditions of existence do not necessitate any considerable 
mutual dependence of parts — where the near approach of the 
plant to its medium in specific gravity, precludes the need of 
a well-developed stem, and where all the materials of growth 
being derived from the water by each portion of the thallus, 
there requires no apparatus for transferring materials from 
part to part. Among animals which, with but few 


exceptions, are, by the conditions of their existence, required 
to take in nutriment through one specialized part of the 
body, it is clear that there must be a means whereby other 
parts of the body, to be supported by this nutriment, must 
have it conveyed to them. It is clear that for an equally 
efficient maintenance of their nutrition, the parts of a large 
mass must have a more elaborate propelling and conducting 
apparatus ; and that in proportion as these parts undergo 
greater waste, a yet higher development of the vascular 
system is necessitated. Similarly with the pre-requisites to 
those mechanical motions which animals are required to 
perform. The parts of a mass cannot be made to move, and 
have their movements so co-ordinated as to produce locomo- 
tive and other actions, without certain structural arrange- 
ments ; and, other things equal, a given amount of such 
activity requires more involved structural arrangements in a 
large mass than in a small one. There must at least be a 
co-ordinating apparatus presenting greater contrasts in its 
central and peripheral parts. 

The qualified dependence of growth on organization, is 
equally implied when we study it in connexion with that 
adjustment of inner to outer relations which constitutes Life. 
In plants this is not conspicuous, because the adjustment of 
inner to outer relations is but- small. Still, it is visible in the 
fact that the condition on which only^a plant can grow to a 
great size, is, that it shall, by the development of a massive 
trunk, present inner relations of forces fitted to counter- 
balance those outer relations of forces, which tend continually 
and occasionally to overthrow it ; and this formation of a 
core of regularly-arranged woody fibres, is an advance in 
organization. Throughout the animal kingdom, this 

connexion of phenomena is manifest. To obtain materials for 
growth ; to avoid injuries, which interfere with growth ; and 
to escape those enemies which bring growth to a sudden end ; 
implies in the organism, the means of fitting its movements 
to meet numerous external co-existences and sequences — 

GROWl'H. 119 

implies such various structural arrangements as sball make 
possible these yariously-adapted actions. It cannot be 
questioned that, everything else remaining constant, a more 
complex animal, capable of adjusting its conduct to a greater 
number of surrounding contingences, will be the better able 
to secure food and evade damage, and so to increase bulk. 
And evidently, without any qualification, we may say that a 
large animal, living under such complex conditions of exist- 
ence as everywhere obtain, is not possible without compara- 
tively high organization. 

While, then, this relation is traversed and obscured by 
sundry other relations, it cannot but exist. Deductively we 
see that it must be modified, as inductively we saw that it is 
modified, by the circumstances amid which each kind of or- 
ganism is placed ; but that it is always a factor in determin- 
ing the result. 

I 45. That growth is, ccBteris paribus, dependent on the sup- 
ply of assimilable matter, is a proposition so continually illus- 
trated by special experience, as well as so obvious from general 
experience, that it would scarcely need stating, were it not re- 
quisite to notice the qualifications with which it must be taken. 

The materials which each organism requires for building 
itself up, are not of one kind, but of several kinds. As a 
vehicle for transferring matter through their structures, aU 
organisms require water as well as solid constituents ; and how- 
ever abundant the solid constituents, there can be no growth 
in the absence of water. Among the solids supplied, there 
•must be a proportion ranging within certain limits. A 
plant round which carbonic acid, water, and ammonia exist 
in the right quantities, may yet be arrested in its growth by 
a deficiency of silica. The total absence of lime from its 
food, may stop the formation of a mammal's skeleton : thus 
dwarfing, if not eventually destroying, the mammal; and 
this, no matter what quantities of other needful colloids and 
crystalloids are furnished. 


Again, the truth that, other things equal, growth varies 
according to the supply of nutriment, has to be qualified by 
the condition, that the supply shall not exceed the ability to 
appropriate it. In the vegetal kingdom, the assimilating 
surface being external, and admitting of rapid expansion by 
the formation of new roots, shoots, and leaves, the effect of 
this limitation is not conspicuous : by artificially supplying 
plants with those materials which they have usually the most 
difficulty in obtaining, we can greatly facilitate their growth; 
and so can produce striking differences of size in the same 
species. Even here, however, the effect is confined within 
the limits of the ability to appropriate ; since in the absence 
of that solar light and heat, by the help of which the chief 
appropriation is carried on, the additional materials of 
growth are useless. In the animal kingdom this 

restriction is rigorous. The absorbent surface being, in the 
great majority of cases, internal ; having a comparatively 
small area, which cannot be greatly enlarged without re- 
construction of the whole body ; and being in connexion 
with a vascular system, which must also be re-constructed 
before any considerable increase of nutriment can be made 
available ; it is clear that beyond a certain point, very soon 
reached, increase of nutriment will not cause increase of 
growth. On the contrary, if the quantity of nutriment 
taken in, is greatly beyond the absorbent power, the excess, 
becoming an obstacle to the regular working of the organism, 
may retard growth rather than advance it. 

While then it is certain, a priori^ that there cannot be 
growth in the absence of such substances as those of which 
an organism consists ; and while it is equally certain that the 
amoimt of growth must primarily be governed by the supply 
of these substances ; it is not less certain that extra supply 
will not produce extra growth, beyond a point very soon 
reached. Deduction shows to be necessary, as induction 
makes familiar, the truths that, the value of food for purposes 
of growth depends not on the quantity of the various 

GROWlll. 121 

orgauizable materials it contains, but on the quantity of 
the material most needed ; that given a right proportion of 
materiab^ the pre-existing structure of the organism limits 
their availability ; and that the higher the structure, the 
sooner is this limit reached. 

§ 46. But why should the growth of every organism be 
finally arrested ? Though the rate of increase may, in each 
case, be necessarily restricted within a narrow range of varia- 
tion — though the increment that is possible in a given time, 
cannot exceed a certain amount ; yet why should the incre- 
ments decrease, and finally become insensible ? Why should 
not all organisms, when supplied with sufficient materials, 
continue to grow as long as they live ? To find an answer 
to this question, we must first revert to the nature and 
functions of organic matter. 

In the first three chapters of Part I., it was shown that 
plants and animals mainly consist of substcmces in states of 
unstable equilibrium —substances which have been raised to 
this unstable equilibrium by the expenditure of the forces we 
know as solar radiations, and which give out these forces in 
other forms, on falling into states of stable equilibrium. 
Leaving out the water, which serves as a vehicle for these 
materials and a medium for their changes ; and excluding 
those mineral matters that play either passive or subsidiary 
parts ; organisms are built up of compounds which are stores 
of force. Those complex colloids and crystalloids which, as 
imited together, form organized bodies, are the same colloids 
and crystalloids which give out, on their decomposition, the 
forces expended by organized bodies. Thus these 

nitrogeneous and carbonaceous substances, being at once 
the materials for organic growth and the sources of organic 
force ; it results that as much of them as is used up for the, 
genesis of force, is taken away from the means of growth ; 
and as much as is economized by diminishing the genesis of 
force, is available for growth. Given that limited quantity 


of nutritive matter which the pre-existing structure of an 
organism enables it to absorb ; and it is a necessary corollary 
from the persistence of force, that the matter accumulated as 
growth, cannot exceed that surplus which remains imde- 
composed, after the production of the required amounts of 
sensible and insensible motion. This, which would 

be rigorously true under all conditions, if exactly the same 
substances were used in exactly the same proportions, for the 
production of force and for the formation of tissue, requires, 
however, to be taken with the qualification, that some of the 
force-evolving substances are not constituents of tissue ; and 
that thus, there may be a genesis of force which is not at the 
expense of potential growth. But since organisms (or at 
least animal organisms, with which we are here chiefly 
concerned,) have a certain power of selective absorption, 
which, partially in an individual and more completely in a 
race, adapts the proportions of the substances absorbed to the 
needs of the system ; then if a certain habitual expenditure 
of force, leads to a certain habitual absorption of force- 
evolving matters that are not available for growth ; and if, 
were there less need for such matters, the ability to absorb 
matters available for growth would be increased to an equi- 
valent extent ; it follows that the antagonism described, does, 
in the long run, hold even without this qualification. Hence, 
growth is substantially equivalent to the absorbed nutriment, 
minus the nutriment used up in action. 

This, however, is no answer to the question — ^why has 
individual growth a limit P The antagonism described, does 
not manifestly account for the fact, that in every domestic 
animal the increments of growth bear continually decreasing 
ratios to the mass, and finally come to an end. Nevertheless, 
it is demonstrable that the excess of absorbed over expended 
nutriment, must, other things equal, become less as the size of 
the animal becomes greater. In similarly-shaped bodies, 

the masses vary as the cubes of the dimensions ; whereas the 
strengths vary as the squares of the dimensions. See here 

GRO^\TII. 123 

the solution of the problem. Supposing a creature which a 
year ago was one foot high, has now become two feet high, 
while it is unchanged in proportions and structure ; what are 
the necessary concomitant changes that have taken place in 
it P It is eight times as heavy ; that is to say, it has to re- 
sist eight times the strain which gravitation puts on its 
structure ; and in producing, as well as in arresting, every 
one of its movements, it has to overcome eight times the 
inertia. Meanwhile, the muscles and bones have sever- 
ally increased their contractile and resisting powers in pro- 
portion to the areas of their transverse sections ; and hence 
are severally but four times as strong as they were. Thus, 
while the creature has doubled in height, and while its ability 
to overcome forces has quadrupled, the forces it has to overcome 
have grown eight times as great. Hence, to raise its body 
through a given space, its muscles have to be contracted with 
twice the intensity, at a double cost of matter expended. This 
necessity will be seen still more clearly if we leave out the 
motor apparatus, and consider only the forces required and 
the means of supplying them. For since, in similar bodies, 
the areas vary as the squares of the dimensions, and the 
masses vary as the cubes ; it follows that the absorbing sur- 
face has become four times as great, while the weight to be 
moved by the matter absorbed has become eight times as 
great. K then, a year ago, the absorbing surface could take 
up twice as much nutriment as was needed for expenditure, 
thus leaving one-half for growth, it is now able only just to 
meet expenditure, and can provide nothing for growth. How- 
ever great the excess of assimilation over waste, may be dur- 
ing the early life of an active organism, we see that because 
a series of numbers increasing as the cubes, overtakes a series 
increasing as the squares, even though starting from a much 
smaller number, there must be reached, if the organism lives 
long enough, a point at which the surplus assimilation is 
brought down to nothing— a point at which expenditure ba- 
lances nutrition: — a state of moving equilibrium. This, 


however, though the chief, is not the sole, varying relation be- 
tween degrees of growth and amountsof expended force. Tliere 
are two more ; one of which conspires with the last, while 
the other conflicts with it. Consider in the first place, the 
cost at which nutriment is distributed through the body, and 
effete matters removed from it. Each increment of growth 
being added at the periphery of the organism, the force ex- 
pended in the transfer of matter must increase in a rapid 
progression — a progression more rapid than that of the mass. 
But as the dynamic expense of distribution is small compared 
with the dynamic value of the materials distributed, this item 
in the calculation is unimportant. Now consider, in the 
second place, the changing proportion between production 
and loss of heat. In similar organisms, the quantities of heat 
generated by similar actions going on throughout their sub- 
stance, must increase as the masses, or as the cubes of the 
dimensions. Meanwhile, the surfaces from which loss of heat 
by radiation takes place, increase only as the squares of the 
dimensions. Though the loss of heat does not therefore in- 
crease only as the squares of the dimensions, it certainly in- 
creases at a smaller rate than the cubes. And to the extent 
that augmentation of mass results in a greater retention of 
heat, it effects an economization of force. This advantage is 
not, however, so important as at first appears. Organic heat 
is a concomitant of organic action, and is so abundantly pro- 
duced during action, that the loss of it is then of no conse- 
quence : indeed the loss is often not rapid enough to keep 
the supply from rising to an inconvenient excess. It is only 
in respect of that maintenance of heat which is needful during 
quiescence, that large organisms have an advantage over 
small ones in this relatively diminished loss. Thjis these two 
subsidiary relations between degrees of growth and amounts 
of expended force, being in antagonism with each other, we 
may conclude that their differential result does not greatly 
modify the result of the chief relation previously set forth. 
Any one who proceeds to test this deduction, will find some 

GROWTH. 125 

seeming incongruities between it and certain facts inductively 
established. Lest these should mislead him, it will be well 
to explain them. Throughout the vegetal kingdom, 

he may remark that there is no limit of growth except what 
death entails. Passing over a large proportion of plants 
which never exceed a comparatively small size, because they 
wholly or partially die down at the end of the year; and 
pointing to trees that annually send forth new shoots, even 
when their trunks are hollowed out by decay ; he may ask — 
How does growth happen here to be unlimited ? The answer 
is, that plants are only accumulators ; they are in no apprecia- 
ble degree expenders. As they do not undergo a waste which 
increases as the cubes of the dimensions, while assimilation 
increases as their squares; there is no reason why their 
growth should be arrested by the equilibration of assimilation 
and waste. Again, should he look among animals for an 

exact correspondence between the decreasing increments of 
growth as ascertained by observation and as determined by de- 
duction, he will not find it. And there are sufficient reasons 
why the correspondence cannot be more than approximate. 
Besides the fact above noted, that there are other varying 
relations which complicate the chief one, he must bear in 
mind that the bodies compared are not truly similar : the 
proportions of trunk to limbs and trunk to head, vary con- 
siderably. The comparison is still more seriously vitiated by 
the inconstant ratio between the constituents of which the 
body is' composed. In the flesh of adult mammalia, water 
forms from 68 to 71 per cent., organic substance from 24 to 
28 per cent., and inorganic substance from 3 to 6 per cent.; 
whereas in the foetal state, the water amoimts to 87 per cent., 
and the solid organic constituents to only 11 per cent. Clearly 
this change from a state in which the force-evolving matter 
forms one tenth of the whole, to a state in which it forms two 
and a half tenths, must greatly interfere with the parallelism 
between the actual and the theoretical progression. Yet 

another difficulty may come under his notice. The crocodile 


is said to grow as long as it lives ; and there appears reason 
to think that some predaceous fishes, such as the pike, do 
the same. That these animals of comparatively high organ- 
ization, have no definite limits of growth, is, however, an ex- 
ceptional fact due to the exceptional non-fulfilment of those 
conditions which entail limitation. What kind of life does 
a crocodile leadP It is a cold-blooded, or almost cold- 
blooded, creature ; that is, it expends very little for the main- 
tenance of heat. It is habitually inert: not chasing prey, but 
lying in wait for it ; and imdergoes considerable exertion 
only during its occasional brief contests with prey. Such 
other exertion as is, at intervals, needful for moving from 
place to place, is rendered small by the small difference 
between the animal's specific gravity and that of water. 
Thus the crocodile expends in muscular action, an amount of 
force that is insignificant compared with the force commonly 
expended by land-animals. Hence its habitual assimilation 
is diminished much less than usual by habitual waste ; and 
beginning with an excessive disproportion between the two, 
it is quite possible for the one never quite to lose its advance 
over the other while life continues. On looking closer into 
such cases as thi^ and that of the pike, which is similarly 
cold-blooded, similarly lies in wait, and is similarly able to 
obtain larger and larger kinds of prey as it increases in size ; 
we discover a further reason for this absence of a definite 
limit. The mechanical causes necessitating a limit, are here 
only partially in action. For a creature living in a medium 
of nearly the same density as its body, has not constantly to 
overcome that gravitative force which is the chief resistance 
to be met by terrestrial animals : it has not to expend for 
this purpose, a muscular power that is large at the outset, and 
increases as the cubes of its dimensions. The only force in- 
creasing as the cubes of its dimensions, which it has thus to 
overcome, is the inertia of its parts. The exceptional con- 
tinuance of growth observed in creatures so circumstanced, is 
therefore perfectly explicable. 

GROWTH. 127 

§ 47. Obviously this antagonism between accumulation and 
expenditure, must be a leading c^use of the contrasts in size 
between allied organisms that are in many respects similarly 
conditioned. The life followed by each kind of animal, is 
one involving a certain average amount of exertion for the 
obtainment of a given amount of nutriment — an exertion, 
part of which goes to the gathering or catching of food, part 
to the tearing and mastication of it, and part to the after- 
processes requisite for separating the nutritive atoms — an 
exertion which therefore varies according as the food is abund- 
ant or scarce, fixed or moving, according as it is mechani- 
cally easy or difficult to deal with when secured, and accord- 
ing as it is, or is not, readily soluble. Hence, while among 
animals of the same species having the same mode of life, 
there will be a tolerably constant ratio between accumulation 
and expenditure, and therefore a tolerably constant limit of 
growth ; there is every reason to expect that different species, 
following different modes of life, will have unlike ratios be- 
tween accumulation and expenditure, and therefore unlike 
limits of growth. 

Though the facts as inductively established, show a general 
harmony with this deduction, we cannot usually trace this 
harmony in any specific way ; since the conflicting and con- 
spiring causes which affect growth are so numerous. The 
only contrast which seems fairly to the point, is the before- 
named one between the vertebrates which fly, and the most 
nearly-allied vertebrates which do not fly: the differences 
in degrees of organization and relations to food, being not such 
as seriously to affect the comparison. If it be admitted that 
birds habitually expend more force than mammals and rep- 
tiles, then it will follow d priori, that, other things being 
tolerably equal, they should have a lower limit of growth 
than mammals and reptiles ; and this we know to be the fact 
d, posteriori. 

§ 48. One of the chief causes, if not the chief cause, of 


the differences between the sizes of organisms, has yet to be 
considered. We are introduced to it by pushing the above 
inquiry a little further. Small animals have been shown to 
possess an advantage over large ones, in the greater ratio 
which, other things equal, assimilation bears to expenditure; 
and we have seen that hence, small animals in becoming 
large ones, gradually lose that surplus of assimilative power 
which they had, and eventually cannot assimilate more than 
is required to balance waste. But how come these animals 
while young and small, to have surplus assimilative powers ? 
Have all animals equal surplus of assimilative powers? 
And if not, how far do differences between the surpluses de- 
termine differences between the limits of growth P We 
shall find in the answers to these questions, the interpretation 
of many marked contrasts in growth that are not due to any 
of the causes above assigned. For example, an ox immensely 
exceeds a sheep in mass. Yet the two live from generation 
to generation in the same fields, eat the same grass and tur- 
nips, obtain these aliments with the same small expenditure 
of force, and differ scarcely at all in their degrees of organiz- 
ation. Whence arises, then, their striking unlikeness of bulk ? 

We noted when studying the phenomena of growth in- 
ductively, that organisms of the larger and higher types, com- 
mence their separate existences, as masses of organic matter 
having tolerable magnitudes. Speaking generally, we saw 
that throughout each organic sub-kingdom, the acquire- 
ment of great bulk occurs only where the incipient bulk 
and organization are considerable; and that they are the 
more considerable in proportion to the complexity of the life 
which the organism is to lead. 

The deductive interpretation of this induction may best be 
commenced by an analogy. A street orange- vendor makes 
but a trifling profit on each transaction; and imless more 
than ordinarily fortunate, he is unable to realize during 
the day a larger amount than will meet his wants : leav- 
ing him to start on the morrow in the same condition as 

GROWTH. 129 

before. The trade of the huxter in ounces of tea and half- 
pounds of sugar, is one similarly entailing much labour for 
small returns. Beginning with a capital of a few pounds, it 
is impossible for him to have a shop large enough, or goods 
sufficiently abundant and various, to permit an extensive 
business : he must be content with the half-pence and pence 
which he makes by little sales to poor people ; and if, avoid- 
ing bad debts, he is able by strict economy to accumulate 
anything, it can be but a trifle. A large retail trader is 
obliged to lay out much money in fitting up an adequate 
establishment ; he must invest a still greater sum in stock ; 
and he must have a further floating capital to meet the 
charges that fall due before his returns come in. Setting 
out, however, with means enough for these purposes, he is 
able to make numerous and comparatively large sales ; and 
so to get greater and more numerous increments of profit. 
Similarly, to get returns in thousands, merchants and manu- 
facturers must make their investments in tens of thousands. 
In brief, the rate at which a man's wealth accumulates, is 
measured by the surplus of income over expenditure ; and 
this, save in exceptionably favourable cases, is determined by 
the capital with which he begins business. Now ap- 

plying the analogy, we may trace in the transactions of an 
organism, the same three ultimate elements. There is the 
expenditure required for the obtainment and digestion of 
food ; there is the gross return in the shape of nutriment as- 
similated, or fit for assimilation ; and there is the difference 
between this gross return of nutriment and the nutriment 
that was used up in the labour of securing it — a difference 
which may be a profit or a loss. Clearly, however, a surplus 
implies that the force expended is less than the force latent 
in the assimilated food. Clearly, too, the increment of 
growth is limited to the amount of this surplus of income 
over expenditure ; so that large growth implies both that the 
excess of nutrition over waste shall be relatively considerable, 
and that the waste and nutrition shall be on extensive scales. 



And clearly, the ability of an organism to expend largely and 
assimilate largely, so as to make a large surplus, presupposes 
a large physiological capital, in the shape of organic matter 
more or less complete in its structural arrangements. 

Throughout the vegetal kingdom, the illustrations of this 
truth are not conspicuous and regular : the obvious reason 
being, that since plants are accumulators and in so small a 
degree expenders, the premises of the above argument are 
but very partially fulfilled. The food of plants (excepting 
Fungi and certain parasites) being in a great measure the 
same for all, and bathing all so that it can be absorbed with- 
out effort, their vital processes result almost entirely in profit. 
Once fairly rooted in a fit place, a plant may thus from the 
outset add its entire returns to capital ; and may soon be able 
to carry on its processes on a large scale, though it does not 
at first do so. When, however, plants are expenders, namely, 
during their germination and first stages of growth, their 
degrees of growth are determined by their amounts of vital 
capital. It LB because the young tree commences life with a 
ready-formed embryo and store of food sufficient to last for 
some time, that it is enabled to strike root and lift its head 
above the surrounding herbage. Throughout the 

animal kingdom, however, the necessity of this relation is 
everywhere obvious. The small carnivore preying on small 
herbivores, can increase in size only by small increments : its 
organization unfitting it to digest larger creatures, even if it 
can kill them, it cannot profit by amounts of nutriment ex- 
ceeding a narrow limit; and its possible increments of growth 
being small to set out with, and rapidly decreasing, must 
come to an end before any considerable size is attained. 
Manifestly the young lion, bom of tolerable bulk, suckled un- 
til much bigger, and fed until half-grown, is enabled by the 
power and organization which he thus gets gratis, to catch 
and kill animals of size enough to give him the large supply 
of nutriment needed to meet his large expenditure, and yet 
leave a large surplus for growth. Thus then is explained 

GROWTH. 131 

the above-named contrast between the ox and the sheep. A 
calf and a lamb commence their physiological transactions on 
widely different scales ; their first increments of growth are 
similarly contrasted in their amounts ; and the two diminish- 
ing series of such increments, end at similarly-contrasted 

§ 49. Such are the several conditions by which the phe- 
nomena of growth are governed. Conspiring and conflicting 
in endless diffei^nt ways and degrees, they in every case 
qualify more or less differently each other's effects. Hence 
it happens that we are obliged to state each generalization as 
true on the average, or to make the proviso— other things 

Understood, in this qualified form, our conclusions are 
these. First, that growth being an integration with the 
organism, of such environing matters as are of like nature 
with the matters composing the organism, its growth is de- 
pendent on the available supply of such matters : this is alike 
a truth established by experience, and an inference from the 
truth given in our forms of thought (First Prtncipks, § 67). 
Second, that the available supply of assimilable matter being 
the same, and other conditions not dissimilar, the degree of 
growth varies according to the surplus of nutrition over ex- 
penditure — a generalization which is illustrated in some of 
the broader contrasts between different divisions of organ- 
isms, and is a direct corollary from the persistence of force. 
Third, that in the same organism, the surplus of nutrition 
over expenditure is a variable quantity ; and that growth is 
unlimited or has a definite Kmit, according as the surplus 
does or does not progressively decrease. This proposition we 
found on the one hand exemplified by the unceasing growth 
of organisms that do not expend force ; by the growth, slowly 
diminishing but never completely ceasing, of organisms that 
expend comparatively little force; and by the definitely 
limited growth of organisms that expend much force ; and 


on the other hand, we found it to follow from a certain rela- 
tive increase of expenditure that necessarily accompanies in- 
crease of btdk, and to be therefore an indirect corollary from 
the persistence of force. Fourth, that among organisms 
which are large expenders of force, the size ultimately at- 
tained is, other things equal, determined by the initial size : 
in proof of which conclusion we have abundant facts, as well 
as the a priori necessity that the sum-totals of analogous 
diminishing series, must depend upon the amounts of their 
initial terms. Fifth, that where the likeness of other cir- 
cumstances permits a comparison, the possible extent of 
growth depends on the degree of organization : an inference 
testified to by the larger forms among the various divisions 
and sub-divisions of organisms ; and inferable d priori from 
the conditions of existence. 



§ 50. Certain general aspects of Development may be 
studied apart from any examination of internal structures. 
These fundamental contrasts between the modes of arrange- 
ment of parts, originating, as they do, the leading external 
distinctions among the various forms of organization, wiU be 
best dealt with at the outset. If all organisms have arisen 
by Evolution, it is of course not to be expected that such 
several modes of development can be absolutely demarcated : 
we may be sure of finding them united by transitional modes. 
But premising that a classification of modes can but approx- 
imately represent the facts, we shall find our genei*al con- 
ceptions of Development aided by one. 

Development is primarily central. All organic forms of 
which the entire history is known, set out with a symmetri- 
cal arrangement of parts roimd a centre. In organisms of 
the lowest grade, no other mode of arrangement is ever 
definitely established ; and in the highest organisms, central 
development, though subordinate to another mode of de- 
velopment, continues to be habitually shown in the changes of 

* In ordinary speech, Development is often used as synonymous with Growth. 
It hence seems needfal to say, that Deyelopment as here and hereafter used, 
means increase of structure, and not increase of hulk. It may he added, that the 
word Evolution, comprehending Growth as well as Development, is to be reserved 
for occasions when both are implied. 


minute structure. Let us glance at these propositions in the 
concrete. Leaving out those Khizopods which are 

wholly structureless, every plant and animal in its earliest 
stage, consists of a spherical sac, full of liquid containing 
organic matter, in which is suspended a nucleated cell, more 
or less distinct from the rest; and the first changes that 
occur in the germ thus constituted, are changes that take 
place round centres produced by division of the original 
centre. From this type of structure, the simplest organisms 
do not depart ; or depart in no definite or conspicuous ways. 
Among plants, the Uredo and the several tribes of Protococci 
permanently maintain such a central distribution; while 
among animals, it is permanently maintained by crea- 
tures like the Gregarina^ and in a difierent manner by the 
Amceba, Adinophrys^ and their allies. In larger organisms, 
made up chiefly of units that are analogous in structure to 
these simplest organisms, the formation of units ever continues 
to take place round points or nuclei ; though the arrangement 
of these imits into groups and wholes may proceed after 
another method. 

Central development may be distinguished into unicentral 
and muUicentral ; according as the product of the original 
germ, develops symmetrically round one centre, or develops 
without subordination to one centre — develops, that is, in 
subordination to many centres. Unicentral de- 

velopment, as displayed not in the formation of single cells 
but in the formation of aggregates, is not common. The 
animal kingdom shows it only in the small group named 
Thalassicollce : inert, spherical masses of jelly, with scarcely 
any organization, which are found floating in southern seas. 
It is feebly represented in the vegetal kingdom by the VoU 
vox glohator. On the other hand, multicentral devel- 

opment, or development roimd insubordinate centres, is va- 
riously exemplified in both divisions of the organic world. It 
is exemplified in two distinct ways, according as the insubor- 
dination among the centres of development is partial or total. 


We may most conyeniently consider it under the heads hence 

Total insubordination among the centres of development^ 
is shown where the units or cells, as fast as they are severally 
formed, part company and lead independent lives. This, in 
the vegetal kingdom, habitually occurs among the Proto- 
phyta; and in the animal kingdom, among the Proto" 
zoa. Partial insubordination is seen in those 

somewhat advanced organisms, that consist of units which, 
though they have not separated, have so little mutual depend- 
ence that the aggregate they form is irregular. Among 
plants, the Thallogens very generally exemplify this mode of 
development. Lichens, spreading with flat or corrugated 
edges in this or that direction, as the conditions determine^ 
have no manifest co-ordination of parts. In the Algce, the 
Nostocs similarly show us an unsymmetrical structure. Of 
Fungif the sessile and creeping kinds display no further 
dependence of one part on another, than is implied by their 
cohesion. And even in such better-organized plants as the 
Marchantiay the general arrangement shows no reference to a 
directive centre. Among animals, many of the Sponges may 
be cited as being thus devoid of that co-ordination implied 
by symmetry: the AmsBba-like imits composing them, though 
they have some subordination to local centres, have no subor- 
dination to a general centre. To distinguish that 
kind of development in which the whole product of a germ 
coheres in one mass, from that kind of development in which 
it does not, Professor Huxley has introduced the words " con- 
tinuous '* and " discantinuom ;" and these seem the best fitted 
for the purpose. Multicentral development, then, is divisible 
into continuous and discontinuous. 

From central development we pass insensibly to that higher 
kind of development for which axial seems the most appro- 
priate name. A tendency towards this is vaguely manifested 
almost everywhere. The great majority even of Protophyta 
and Protozoa have difierent longitudinal and transverse di- 


mensioiis — have an obscure if not a distinct axial structure. 
The originally cellular units out of which higher organisms 
are mainly built up, usually pass into shapes that are subordi- 
nated to lines rather than to points. And in the higher organ- 
isms, considered as wholes, an arrangement of parts in rela- 
tion to an axis is distinct and nearly universal. We see it in 
the superior orders of Thallogens ; and in all the Acrogens, 
Endogens, and Exogens. With few exceptions the Coeknte- 
rata clearly exhibit it ; it is traceable, though less conspicu- 
ously, throughout the MolluBca; and the Annuhsa and 
Vertebrata uniformly show it with perfect definiteness. 

This kind of development, like the first kind, is of two 
orders. The whole germ-product may arrange itself round 
a single axis, or it may arrange itself round many axes ; the 
structure may be uniaxial or multiaxial. Each division of 
the organic kingdom furnishes examples of both these or- 
ders. In such Fangi as exhibit axial development at 
all, we commonly see development round a single axis. Some 
of the AlgcBy as the common tangle, show us this arrange- 
ment. And of the higher plants, many Endogens and 
small Exogens are uniaxial. Of animals, the advanced are 
without exception in this category. There is no known ver- 
tebrate in which the whole of the germ-product is not subor- 
dinated to a single axis. In the more fully-organized Annu- 
hsa, the like is almost universal ; as it is also in the superior 
orders of Mollusca. Multiaxial development occurs 
in most of the plants we are familiar with — every branch of 
a shrub or tree being an independent axis. But while in the 
vegetal kingdom, multiaxial development prevails among the 
highest types; in the animal kingdom, it prevails only among 
the lowest types. It is extremely general, if not universal, 
among the Ccdenterata ; it is characteristic of the Mollus- 
coida ; among Molluscs the compound Ascidians exhibit it ; 
and it is seen, though under another form, in the inferior 

Development that is axial, like development that is central, 


may be either continuous or discontinuous : the parts having 
different axes may continue united, or they may separate. 
Instances of each alternative are supplied by both plants 
and animals. Continuous, multiaxial development, is 

that which plants usually display ; and need not be illustrated 
further than by reference to every garden. As cases of it in 
animals may be named, all the compoimd Hydrozoa and Ac" 
tinozoa; and such molluscous forms as the BotryllidcB, Of 

multiaxial development that is discontinuous, a familiar 
instance among plants exists in the conmion strawberry. 
This sends out over the neighbouring surface, long slender 
shoots, bearing at their extremities buds that presently strike 
roots, and become new individuals ; and these by and by lose 
their connexions with the original axis. Other plants there 
are that produce certain specialized buds called bulbils, which 
separating themselves and falling to the ground, grow into 
independent plants. Among animals the fresh-water polype 
very clearly shows this mode of development : the young 
polypes, budding out from its surface, severally arrange 
their parts around distinct axes, and eventually detaching 
themselves, lead separate lives, and produce other polypes 
after the same fashion. By some of the lower Annulom, this 
multiplication of axes from an original axis, is carried on after 
a different manner : the string of segments spontaneously 
divides ; and after further growth, division recurs in one or 
both of the halves. And in the Aphides, we have a still fiu> 
ther modification of this process. 

Grouping together its several modes as above delineated, 
we see that 

r Unicentral 
Central j or r Continuous 

Development is < or 

Multicentral \ or 

C Discontinuous 

C Uniaxial 
Axial j or r Continuous 

^ Multiaxial \ or 

'^ Discontinuous 


Any one adequately acquainted with the facts^ may readily 
raise objections to this arrangement. He may name forms 
which do not obviously come under any of these heads. He may 
point to plants that are for a time multicentral, but after- 
wards develop axially. And from lower types of animals, he 
may choose many in which the continuous and discontinuous 
modes are both displayed. But, as already hinted, an ar- 
rangement free from such anomalies must be impossible, if the 
various orders of organization have arisen by Evolution. The 
one above sketched out, is to be regarded as only a rough 
grouping of the facts, which helps us to a conception of them 
in their totality ; and so regarded, it will be of service when 
we come to treat of Individuality and Beproduction. 

§ 51. From these most general external aspects of organic 
development, let us now turn to its internal and more special 
aspects. When treating of Evolution as a universal process 
of things, a rude outline of the course of structural changes in 
organisms was given {First Principles, §§ 43, 65, 66). Here, 
however, it will be proper to describe these changes more fully. 

The bud of any common plant in its earliest stage, consists 
of a small hemispherical or sub-conical projection. While 
it increases most rapidly at the apex, this presently deve- 
lops on one side of its base, a smaller projection of like general 
shape with itself. Here is the rudiment of a leaf ; which pre- 
sently spreads more or less roimd the base of the central 
hemisphere or main axis. At the same time that the central 
hemisphere rises higher, this lateral prominence, also in- 
creasing, gives rise to subordinate prominences or lobes. 
These are the rudiments of stipules, where the leaves are 
stipulated. Meanwhile, towards the other side of the main 
axis, and somewhat higher up, another lateral prominence 
arising, marks the origin of a second leaf. By the time that 
the first leaf has produced another pair of lobes, and the 
second leaf has produced its primary pair, the central hemi- 
sphere, still increasing at its apex, exhibits the rudiment of a 


third leaf. Similarly throughout. While the germ of each 
succeeding leaf thus arises, the germs of the previous leaves, 
in the order of their priority, are changing their rude nodu- 
lated shapes into flattened-out expansions ; which slowly put 
on those sharp outlines they show when unfolded. Thus 
from that extremely indefinite figure, a rounded lump, giving 
off from time to time lateral lumps, which severally becoming 
symmetrically lobed, gradually assume specific and involved 
forms, we pass little by little to that comparatively complex 
thing — ^a leaf-bearing dioot. Internally, a bud under- 

goes analogous changes. The layer of substance which forms 
the surface of the hemisphere, and in which these metamor- 
phoses commence, consists of a transparent, irregularly-aggre- 
gated mass of cells and centres of growth, not formed into a 
tissue. Especially is this the case at the apex, where the 
vital activity is the greatest. Here the primitive cellular 
mass passes without any line of demarcation into the tissues 
that are developing from it. While, by continued cell-multi- 
. plication this layer increases, and doing so most rapidly at 
the apex thrusts outwards its lateral portions, these begin to 
exhibit differentiations. " Gradually," says Schleiden, " se- 
parate masses of cells, with a distinct and definite outline, 
appear in this chaos, and they cease to partake of the process 
of growth going on. At first the epidermis is separated, 
then the vascular bundles, later the parenchyma." Similarly 
with the lateral buds whence leaves arise. In the, at first, un- 
organized mass of cells constituting the rudimentary leaf, 
there are formed vascular bundles which eventually become 
the veins of the leaf ; and gradually there appear also, though 
in ways that have not been specified, the parenchyma and the 
epithelium. Nor do we fail to find an essentially 

parallel set of changes, when we trace the histories of the in- 
dividual cells. While the tissues they compose are separ- 
ating, the cells are growing step by step more unlike. 
Some become flat, some polyhedral, some cylindrical, some 
piismatie, some spindle-shaped. These develop spiral fibres 


in their interiors ; and those, net- works of fibres. Here a 
number of cells unite together to form a tube; and there 
they become solid by the internal deposition of woody or other 
matter. Through such changes, too numerous and involved 
to be here detailed, the originally uniform cells go on diverg- 
ing and re-diverging, until there are produced various forms 
that seem to have very little in common. 

The arm of a man makes its first appearance in as simple 
a way as does the shoot of a plant. According to Bischoff, it 
buds-out from the side of the embryo, as a little tongue-shaped 
projection, presenting no differences of parts ; and it might 
serve for the rudiment of some one of the various other organs 
that also arise as buds. Continuing to lengthen, it presently 
becomes somewhat enlarged at its end; and is then described as 
a pedicle bearing a flattened, round-edged lump. This lump is 
the representative of the future hand ; and the pedicle, of the 
future arm. By and by, at the edges of this flattened lump, 
there appear four clefts, dividing &om each other the buds of 
the future fingers ; and the hand as a whole grows a little . 
more distinguishable from the arm. Up to this time, the 
pedicle has remained one continuous piece ; but it now begins 
to show a bend at its centre, which indicates the division into 
arm and forearm. The distinctions thus rudely indicated, 
gradually increase : the fingers elongate and become jointed ; 
and the proportions of all the parts, originally very un- 
like those of the complete limb, slowly approximate to 
them. During its bud-like stage, the rudimentary 

arm is nothing but a homogeneous mass of simple cells, with- 
out any arrangement. By the diverse changes they gradually 
undergo, these cells are transformed into bones, muscles, 
blood-vessels, and nerves. The extreme softness and delicacy 
of this primary cellular tissue, renders it difficult to trace the 
initial stages of these differentiations. In consequence of the 
colour of their contents, the blood-vessels are the first parts to 
become visible. Afterwards the cartilaginous parts, which 
are the bases of the future bones, become marked out by the 


denser aggregation of their constituent cells, and the produc- 
tion between these of a hyaline substance which unites them 
into a translucent mass. When first perceptible, the muscles 
are gelatinous, pale, yellowish, transparent, and indistinguish- 
able from their tendons. The various other tissues of which 
the arm consists, beginning with very faintly-marked differ- 
ences, become day by day more definite in their outlines and 
appearances. In like manner, the units composing 

these tissues, severally assume increasingly-specific characters. 
The fibres of muscle, at first made visible in the midst of 
their gelatinous matrix only by immersion in alcohol, grow 
more numerous and distinct ; and by and by they begin to 
exhibit transverse stripes. The bone-cells put on by degrees 
their curious structure of branching canals. And so in their 
respective ways with the units of skin and the rest. 

Thus in each of the organic sub-kingdoms, we see this 
change from an incoherent, indefinite homogeneity, to a 
coherent, definite heterogeneity, illustrated in a quadruple 
way. The originally -like units or cells, become imlike in 
various ways, and in ways more numerous and marked as the 
development goes on. The several tissues which these 
several classes of cells form by aggregation, grow little by 
little distinct from each other ; and little by little put on 
those structural complexities, that arise from differentiations 
among their component imits. In the shoot, as in the limb, 
the external form, originally very simple, and having much 
in common with countless simple forms, organic and in- 
organic, gradually acquires an increasing complexity, and an 
increasing unlikeness to other forms. And meanwhile, the 
remaining parts of the organism to which the shoot or limb 
belongs, having been severally assuming structures divergent 
from each other and from that of this particular shoot or 
limb, there has arisen a greater heterogeneity in the organ- 
ism as a whole. 

§ 52. One of the most remarkable inductions of embry- 


ology comes next in order. Von Baer found that in ifs 
earliest stage, every organism has the greatest number of 
characters in common with all other organisms in their 
earliest stages ; that at a stage somewhat later, its structure 
is like the structures displayed at corresponding phases by a 
less extensive multitude of organisms ; that at each sub- 
sequent stage, traits are acquired which successively distin- 
guish the developing embryo from groups of embryos that it 
previously resembled— thus step by step diminishing the 
group of embryos which it still resembles ; and that thus the 
class of similar forms, is finally narrowed to the species of 
which it is a member. This abstract proposition will per- 
haps not be fully realized by the general reader. It will be 
best to re-state it in a concrete shape. The germ 

out of which a human being is evolved, differs in no visible 
respect from the germ out of which every animal and plant is 
evolved. The first conspicuous structural change undergone 
by this human germ, is one characterizing the germs of 
animals only — differentiates them from the germs of plants. 
The next distinction established, is a distinction exhibited by 
all Vertebrata; but never exhibited by Annulosa, Mollusca^ or 
Ckeknterata, Instead of continuing to resemble, as it now 
does, the rudiments of all fishes, reptiles, birds, and mammals ; 
this rudiment of a man, assumes a structure that is seen only 
in the rudiments of mammals. Later, the embryo undergoes 
changes which exclude it from the group of implacental 
mammals ; and prove that it belongs to the group of placental 
mammals. Later still, it grows unlike the embryos of those 
placental mammals distinguished as ungulate or hoofed ; and 
continues to resemble only the unguiculate or clawed. By 
and by, it ceases to be like any foetuses but those of the quad- 
rumana; and eventually the foetuses of only the higher 
quadrumana are simulated. Lastly, at birth, the infant, 
belonging to whichever human race it may do, is structurally 
very much like the infants of all other human races; and 
only afterwards acquires those various minor peculiarities of 


form that distinguish the yariety of man to which it be- 

The generalization here expressed and illustrated, must 
not be confounded with an erroneous semblance of it that has 
obtained considerable currency. An impression has been 
given by those who hare popularized the statements of em- 
bryologists^ that during its developmenti each higher organ- 
ism passes through stages in which it resembles the adult 
forms of lower organisms— that the embryo of a man is at 
one time like a fish, and at another time like a reptile. This 
is not the fact. The fact established is, that up to a certain 
point, the embryos of a man and a fish continue similar, and 
that then differences begin to appear and increase — the one 
embryo approaching more and more towards the form of a 
fish ; the other diverging from it more and more. And so 
with the resemblances to the more advanced types. Suppos- 
ing the germs of all kinds of organisms to be simultaneously 
developing, we may say that all members of the vast mul- 
titude take their first steps in the same direction ; that at the 
second step one-half of this vast multitude diverges from the 
other half, and thereafter follows a different course of deve- 
lopment ; that the immense assemblage contained in either 
of these divisions, very soon again shows a tendency to take 
two or more routes of development ; that each of the two or 
more minor assemblages thus resulting, shows for a time but 
small divergences among its members, but presently again 
divides into groups which separate ever more widely as they 
progress ; and so on, until each organism, when nearly com- 
plete, is accompanied in its further modifications only by 
organisms of the same species ; and last of all, assumes the 
peculiarities which distinguish it as an individual— diverges 
to a slight extent to the organisms it is most like. The 

reader must also be cautioned against accepting this general- 
ization as exact. The likenesses thus successively displayed 
are not precise but approximate. Only leading characteris- 
tics are the same : not all the details. It is as though in 


one of the diverging groups just described, each kind of 
organism, though having a general direction of development 
like that of the others it is for a time traveUing with, shows 
from the first a tendency to leave the general route — ^a tend- 
ency which presently becomes strongly marked. Making 
all requisite qualifications, however, these resemblances re- 
main conspicuous ; and the fact that they follow each other 
in the way described, is a fact of great significance. 

§ 53. This comparison between the course of development 
in any creature, and the course of development in all other 
creatures^-this arrival at the conclusion that the course of 
development in each, at first the same as in all others, be- 
comes stage by stage differentiated from the courses of all 
others, brings us within view of an allied conclusion. If we 
contemplate the successive stages passed through by any 
higher organism, and observe the relation between it and its 
environment at each of these stages ; we shall see that this re- 
lation is modified in a way analogous to that in which the 
relation between the organism and its environment is modi- 
fied, as we advance from the lowest to the highest grades. 
Along with the progressing differentiation of each organism 
from others, we find a progressing differentiation of it 
from its environment; like that progressing differentiation 
from the environment which we meet with in the ascending 
forms of life. Let us first glance at the way in which the 
ascending forms of life exhibit this progressing differentiation 
from the environment. 

In the first place, it is illustrated in structure. Ad- 
vance from the homogeneous to the heterogeneous, itself in- 
volves an increasing distinction from the inorganic world. 
In the lowest Protozoa we have a simplicity approaching 
to that of air, water, or earth ; and the ascent to organisms 
of greater and greater complexity of structure, is an ascent to 
organisms that are in that respect more strongly contrasted 
with the structureless environment. In form y again. 


we see the Bame fact An ordinary charaoteristic of inor- 
ganic matter is its indefiniteness of form ; and this is also a 
characteristic of the lower organisms, as compared with the 
higher. Speaking generaUj, plants are less definite than 
animalsy both in shape and size — admit of greater modifica- 
tions firom variations of position and nutrition. Among ani- 
mals, the simplest Bhizopods are not only structureless but 
amorphous : the form is never specific, and is constantly 
changing. Of the organisms resulting from the aggregation 
of such creatures, we see that while some, as the Foramini- 
fera^ assume a certain definiteness of form, in their shells at 
least ; others, as the Sponges, are very irregular. The Zoo- 
phytes and the Polyzoa are compound organisms, most of 
which have a mode of growth not more determinate than that 
of plants. But among the higher animals, we find not 
only that the mature shape of each species is very definite, 
but that the individuals of each species differ very little in 
size. A parallel increase of contrast is seen in chemi- 

cal compmtiofK With but few exceptions, and those only 
partial ones, the lowest animal and vegetal forms are inhabit- 
ants of the water ; and water is almost their sole constituent. 
Desiccated Protophyta and Protozoa shrink into mere dust ; 
and among the Acalephes, we find but a few grains of solid 
matter to a pound of water. The higher aquatic plants, in 
common with the higher aquatic animals, possessing as they 
do increased tenacity of substance, also contain a greater pro- 
portion of the organic elements ; and so are chemically more 
unlike their medium. And when we pass to the superior 
classes of organisms — land-plants and land-animals — we find 
that, chemically considered, they have little in common either 
with the earth on which they stand or the air which sur- 
rounds them. In specific gravity too, we may note 
the like truth. The very simplest forms, in common with 
the spores and gemmules of higher ones, are as nearly as may 
be of the same specific gravity as the water in which they 
float; and though it cannot be said that among aquatic 
* 10 


creatures, superior specific gravity is a standird of general 
superiority, yet we may fairly say that the superior orders of 
them, when divested of the appliances by which their specific 
gravity is regulated, differ more from water in their relative 
weight than do the lowest. In terrestrial organisms, the 
contrast becomes extremely marked. Trees and plants, in 
common with insects, reptiles, mammals, birds, are all of a 
specific gravity considerably less than that of the earth and 
immensely greater than that of the air. Yet further, 

we see the law similarly fulfilled in respect of temperature. 
Plants generate but extremely small quantities of heat, which 
are to be detected only by very delicate experiments ; and 
practically they may be considered as having the same tem- 
perature as their environment. The temperature of aquatic 
animals is very little above that of the surrounding water : 
that of the invertebrata being mostly less than a degree above 
it, and that of fishes not exceeding it by more than two or 
three degrees ; save in the case of some large red-blooded 
fishes, as the tunny, which exceed it in temperature by nearly 
ten degrees. Among insects, the range is from two to ten 
degrees above that of the air : the excess varying according 
to their activity. ITie heat of reptiles is from four to fifteen 
degrees more than the heat of their medium. While mam- 
mals and birds maintain a heat which continues almost un- 
affected by external variations, and is often greater than that 
of the air by seventy, eighty, ninety, and even a hundred 
degrees. Once more, in greater self-mohility a pro- 

gressive differentiation is traceable. The especial character- 
istic by which we distinguish dead matter is its inertness ; 
some form of independent motion is our most general test of 
life. Passing over the indefinite border-land between the 
animal and vegetal kingdoms, we may roughly class plants 
as organisms which, while they exhibit that species of motion 
implied in growth, are not only devoid of locomotive power, 
but with some unimportant exceptions are devoid of the 
power of moving their parts in relation to each other ; and 


thus are lees diflferentiated from the inorganic world than 
animals. Though in those microscopic Protophyta and Pro- 
tozoa inhabiting the water — ^the spores of algae, the gemmules 
of sponges, and the infusoria generally — ^we see locomotion 
produced by ciliary action ; yet this locomotion, while rapid 
relatively to the size of the creatures, is absolutely slow. Of 
the CoBlenterata, a great part are either permanently rooted or 
habitually stationary ; and so have scarcely any self-mobility 
but that implied in the relative movements of parts ; while 
the rest, of which the common jelly-fish will serve as a sam- 
ple, have mostly but little ability to move themselves through 
the water. Among the higher aquatic Invertebrata, — cuttle- 
fishes and lobsters, for instance, — ^there is a very considerable 
power of locomotion ; and the aquatic Vertebrata are, con- 
sidered as a class, much more active in their movements than 
the other inhabitants of the water. But it is only when we 
come to air-breathing creatures, that we find the vital charac- 
teristic of self-mobility manifested in the highest degree. 
Flying insects, mammals, birds, travel with a velocity far 
exceeding that attained by any of the lower classes of ani- 
mals ; and so are more strongly contrasted with their inert 
environment. Thus, on contemplating the various 

grades of organisms in their ascending order, we find them 
more and more distinguished from their inanimate media, in 
structure, in /orw, in chemical composition, in specific gramty, 
in temperature, in self •mobility. It is true that this general- 
ization does not hold with complete regularity. Organisms 
which are in some respects the most strongly contrasted with 
the environing inorganic world, are in other respects less so 
than inferior organisms. As a class, mammals are higher 
than birds ; and yet they are of lower temperature, and have 
smaller powers of locomotion. The stationary oyster is of 
higher organization than the free-swimming medusa ; and 
the cold-blooded and less heterogeneous fish, is quicker in its 
movements than the warm-blooded and more heterogeneous 
eJoth.^^But the admission that the several aspects under 
"^ 10* 


which this increasing contrast shows itself, bear variable 
ratios to each other, does not conflict with the general truth, 
that as we ascend in the hierarchy of organisms, we meet with 
not only an increasing differentiation of parts, but also an 
increasing differentiation from the surrounding medium in 
sundry other physical attributes. It would seem that this 
peculiarity has some necessary connexion with superior 
vital manifestations. One of those lowly gelatinous forms, 
so transparent and colourless as to be with difficulty dis- 
tinguished from the water it floats in, is not more like its 
medium in chemical, mechanical, optical, thermal, and other 
properties, than it is in the passivity with which it sub- 
mits to all the influences and actions brought to bear upon 
it ; while the mammal does not more widely differ from 
inanimate things in these properties, than it does in the ac- 
,tivity with which it meets surrounding changes by compens- 
ating changes in itself. And between these two extremes, 
we shall observe a constant ratio between these two kinds of 
contrast. Whence we may say, that in proportion as an 
organism is physically like its environment, does it remain a 
passive partaker of the changes going on in its environment ; 
while in proportion as it is endowed with powers of coimter- 
acting such changes, it exhibits greater unlikeness to its en- 

If now, from this same point of view, we consider the rela- 
tion borne to its environment by any superior organism in 
its successive stages, we find an analogous series of con- 
trasts. Of course in respect of degrees of structure, the 
parallelism is complete. The difference, at first small, be- 
tween the comparatively structureless germ and the com- 
paratively structureless inorganic world, becomes necessarily 
greater, step by step, as the differentiations of the germ be- 
come more numerous and definite. How of form 
the like holds, is equally manifest. The sphere, which is 

• This paragraph originally formed part of a review-article on " Transcenden- 
tal Physiology^" published in 1857. 


the point of departure common to all organisms^ is the most 
generalized of figures ; and one that is, under various circum- 
stances, assumed by inorganic matter. While the incipient 
organism is spherical, it is not only like many particular in- 
organic masses ; but it is like the rest, in the sense that it has 
the shape which would result, were all their irregularities 
averaged. But as it develops, it loses all likeness to inor- 
ganic objects in the environment ; and eventually becomes 
distinct even from all organic objects in its environ- 
ment. In specific gravity, the alteration, though not 
very marked, is still in the same direction. Development 
being habitually accompanied by a relative decrease in the 
quantity of water, and an increase in the quantity of consti- 
tuents that are heavier than water, there residts a small aug- 
mentation of relative weight. In power of maintain- 
ing a temperature above that of surrounding things, the 
differentiation from the environment that accompanies deve- 
lopment, is marked. All ova are absolutely dependent for 
their heat on external sources. Like inorganic bodies^ they 
gain or lose heat according as neighbouring bodies are colder 
or hotter. The mammalian young is, during its uterine life, 
dependent on the maternal heat ; and at birth has but a par- 
tial power of making good the loss by radiation. But as it 
advances in development, it gains an ability to maintain a 
constant temperature above that of surrounding things : so 
becoming markedly unlike all surrounding things, save or- 
ganisms of allied nature. Lastly, in aelf-mobUity this 
r increasing contrast is not less decided. Save in a few aber- 
rant tribes, chiefly parasitic, we find the general fact to be, 
that the locomotive power, totally absent or very small at the 
outset, increases with the advance towards maturity. The 
more highly developed the organism becomes, the stronger 
grows the contrast between its activity and the inertness of 
the objects amid which it moves. 

Thus we may say that the development of an individual 
organism, is at the same time a differentiation of its parts 


from each other, and a differentiation of the consolidated 
whole from the environment ; and that in the last as in the 
first respect, there is a general analogy between the progres- 
sion of an individaal organism, and the progression from the 
lowest orders of organisms to the highest orders. It 

may be remarked that some kinship seems to exist between 
these generalizations and the doctrine of Schelling, that Life 
is the tendency to individuation. For evidently, in becom- 
ing more distinct from each other, and from their environ- 
ment, organisms acquire more marked individualities.' As 
far as I can gather from outlines of his philosophy, however, 
it appears that Schelling entertained this conception in a 
general and transcendental sense, rather than in a special and 
scientific one. 

§ 54. The deductive interpretations of these general facts 
of development, in so far as they are at present possible, must 
be postponed until we arrive at the fourth and fifth divisions of 
this work ; which will be chiefly occupied with them. There 
are, however, one or two general aspects of these inductions, 
which may be here most conveniently dealt with deductively. 

The general law of development as displayed in organisms, 
is readily shown to be necessary, if the initial and terminal 
stages are such as we know them to be. Grant that each 
organism is at the outset homogeneous, and that when com- 
plete it is relatively heterogeneous ; and of necessity it fol- 
lows that development is a change from the homogeneous 
to the heterogeneous — ^a change during which there must be 
gone through all the infinitesimal gradations of heterogeneity 
that lie between these extremes. If, again, there is at first 
indefiniteness, and at last definiteness, the transition cannot 
but be from the one to the other of these, through all intermedi- 
ate degrees of definiteness. Further, if the parts, originally 
incoherent or uncombined, eventually become relatively co- 
herent or combined; there must be a continuous increase of 
coherence or combination. Hence the general truth that 


development is a change from incoherent, indefinite homo- 
geneity, to coherent, definite heterogeneity, becomes a self- 
evident one, when observation has shown us the state in 
which organisms begin, and the state in which they end. 

Just in the same way that the growth of an entire organ- 
ism, is carried on by abstracting from the environment 
substances like those composing the organism ; so the pro- 
duction of each organ within the organism, -is carried on by 
abstracting from the substances contained in the organism, 
those required by this particular organ. Each organ at the 
expense of the organism as a whole, integrates with itself 
certaui special kinds and proportions of the matters circulat- 
ing around it ; in the same way that the organism as a 
whole, integrates with itself certain special kinds and propor- 
tions of matters at the expense of the environment as a 
whole. So that the organs are qualitatively differentiated 
from each other, in a way analogous to that by which the en- 
tire organism is qualitatively differentiated from things 
around it. Evidently this selective assimilation 

illustrates the general truth, demonstrable a priori, that like 
units tend to segregate. It illustrates, moreover, the further 
aspect of this general truth, that the pre-existence of a mass 
of certain units, produces, probably by polar attraction, a 
tendency for diffused units of the same kind to aggregate 
with this mass, rather than elsewhere. It has been shown of 
particular salts, A and B, co-existing in a solution not suf- 
ficiently concentrated to crystallize, that if a crystal of the salt 
A be put into the solution, it will increase by uniting with itself 
the dissolved atoms of the salt A ; and that similarly, though 
there otherwise takes place no deposition of the salt B, yet if 
a crystal of the salt B is placed in the solution, it will exercise 
a coercive force on the diffused atoms of this salt, and grow at 
their expense. No doubt much organic assimilation occurs 
in the same way. Particular parts of the organism are com- 
posed of special units, or have the function of secreting 
special units, which are ever present in them in large quan- 


tities. The fluids circulating through the body contain 
special units of this same order. And these diffused units 
are continually being deposited along with the groups of like 
units that already exist. How purely physical are the causes 
of this selective assimilation, is, indeed, conclusively shown 
by the fact, that abnormal constituents of the blood are 
segregrated in the same way. Cancer-cells having begun to 
be deposited at a particular place, continue to be deposited at 
that place. Tubercular matter, making its appearance at 
particular points, collects more and more round those points. 
And similarly in numerous pustular diseases. Where 

the component units of an organ, or some of them, do not 
exist as such in the circulating fluids, but are formed out of 
elements or compounds that exist separately in the circulat- 
ing fluids ; it is clear that the process of differential assimil- 
ation is of a more complex kind. StiU, however, it seems 
not impossible that it is carried on in an analogous way. If 
there be an aggregate of compound atoms, each of which 
contains the constituents A, B, C ; and if round this aggre- 
gate the constituents A and B and C are diffused in uncom- 
bined states ; it may be suspected that the coercive polar force 
of these aggregated compound atoms A, B, C, may not only 
bring into union with themselves adjacent compound atoms 
A, B, C, but may cause the adjacent constituents A and B 
and C to unite into such compound atoms, and then aggre- 
gate with the mass. Should this be so, the process of differ- 
ential assimilation, which plays so important a part in 
organic development, will not be difficult to understand. At 
present, however, chemical inquiry appears to have furnished 
no evidence either for or against such an hypothesis. 



§ 65. Does Structure originate Function, or does Func- 
tion originate Structure ? is a question about which there has 
been disagreement. Using the word Function in its widest 
signification, as the totality of all vital actions, the question 
amounts to this — does Life produce Organization, or does 
Organization produce Life P 

To answer this question is not easy, since we habitually 
find the two so associated that neither seems possible without 
the other; and they appear uniformly to increase and 
decrease together. If it be said that the arrangement of or- 
ganic substances in particular forms, cannot be the ultimate 
cause of vital changes, which must depend on the properties 
of such substances ; it may be replied that, in the absence of 
structural arrangements, the forces evolved cannot be so 
directed and combined as to secure that correspondence 
between inner and outer actions which constitutes Life. 
Again, to the allegation that the vital activity of every germ 
whence an organism arises, is obviously antecedent to the 
development of its structures ; there is the answer that such 
germ is not absolutely structureless, but consists of a mass of 
cells, containing a ceU that difiers from the rest, and initiates 
the developmental changes. There is, however, one 

fact implying that Function must be regarded as taking pre- 
cedence of Structure. Of the lowest Rhizopods, which pre- 


sent no distinctions of parts, and nevertheless feed and 
grow and move about, Prof. Huxley has remarked that they 
exhibit Life without Organization. The perpetual changes of 
form which alone distinguish one of these creatures from an 
inanimate fragment, are no doubt totally irregular and un- 
directed. Still they do, through an average of accidents, 
subserve the creatures' nutrition ; and they do imply an ex- 
penditure of force that in some way depends on the consump- 
tion of nutriment. They do, therefore, though in the rudest 
way, display a vital adjustment of internal to external relations. 

§ 56. Function falls into divisions of several kinds, ac- 
cording to our point of view. Let us take these divisions in 
the order of their simplicity. 

Under Function in its widest sense, are included both the 
statical and the dynamical distributions of force which an 
organism opposes to the forces brought to bear on it. In a 
tree, the woody core of trunk and branches, and in an animal, 
the skeleton, internal or external, may be regarded as pas- 
sively resisting the gravity and momentum which tend 
habitually or occasionally to derange the requisite relations 
between the organism and its environment ; and since they 
resist these forces simply by their cohesion, their functions 
may be classed as statical. Conversely, the leaves and sap- 
vessels in a tree, and those organs which in an animal 
similarly carry on nutrition and circulation, as well as those 
which g^ierate and direct muscular motion, must be con- 
sidered as dynamical in their actions. From another 
point of view, Function is divisible into the accumulation of 
force (latent in food) ; the expenditure of force (latent in the 
tissues and certain matters absorbed by them) ; and the 
transfer of force (latent in the prepared nutriment or blood) 
from the parts which accumulate to the parts which expend. 
In plants we see little beyond the first of these : expenditure 
being inappreciable, and transfer required only to facilitate 


accumulation. In animals, the function of accumulation 
comprehends those processes by which the materials contain- 
ing latent force are taken in, digested, and separated from 
other materials ; the fimction of transfer comprehends those 
processes by which these materials, and such others as are 
needful to liberate the forces they contain, are conveyed 
throughout the organism ; and the function of expenditure 
comprehends those processes by which the forces are liberated 
from these materials, and transformed into properly co-ordin- 
ated motions. Each of these three most general 
diyisions, includes several more special divisions. The accu- 
mulation of force may be separated into alimentation and 
aeration ; of which the first is again separable into the 
various acts gone through between prehension of food and 
the transformation of part of it into blood. By the transfer 
of force is to be understood what we call circulation; if the 
meaning of circulation be extended to embrace the duties of 
both the vascular system and the lymphatics. Under the 
head of expenditure of force, come nervous actions and mus- 
cular actions: though not absolutely co-extensive with ex- 
penditure, these are almost so. Lastly, there are the 
subsidiary functions which do not properly fall within any 
of these general functions, but subserve them by removing 
the obstacles to their performance : those, namely, of ex- 
cretion and exhalation^ whereby waste products are got 
rid of. Again, disregarding their purposes and 
considering them analytically, the general physiologist may 
consider functions in their widest sense as the correlatives of 
tissues — ^the actions of epidemic tissue, cartilaginous tissue, 
elastic tissue, connective tissue, osseous tissue, muscular 
tissue, nervous tissue, glandular tissue. Once more, 
physiology in its concrete interpretations, recognizes special 
functions as the ends of special organs — ^regards the teeth as 
having the office of mastication ; the heart as an apparatus 
to propel blood ; this gland as fitted to produce one requisite 


secretion and that to produce another ; each muscle as the 
agent of a particular motion ; each nerve as the vehicle of a 
special sensation or a special motor impulse. 

It is clear that dealing with Biology only in its larger 
aspects, specialities of ftmction do not concern us ; except in 
so far as they serve to illustrate, or to qualify, its general- 

§ 57. The first induction to be here set down, is a 
familiar and obvious one : the induction, namely, that com- 
plexity of function, is the correlative of complexity of struc- 
ture. The leading aspects of this truth must be briefly noted. 

Where there are no distinctions of structure, there are no 
distinctions of function. One of the Rhizopods above 
instanced as exhibiting life without organization, will serve 
as an illustration. From the outside of this creature, 
which has not even a limiting membrane, there are protruded 
numerous thread-like processes. Originating from any point 
of the surface, each of these may contract again and disap- 
pear ; or it may touch some fragment of nutriment, which it 
draws with it, when contracting, into the general mass — ^thus 
serving as hand and mouth ; or it may come in contact with 
its fellow-processes at a distance from the body, and become 
confluent with them ; or it may attach itself to an adjacent 
fixed object, and help by its contraction to draw the body 
into a new position. In brief, this structureless speck of 
animated jelly, is at once all stomach, all skin, all mouth, all 
limb, and doubtless, too, all lung. In organisms 

having a -fixed distribution of parts, there is a concomitant 
fixed distribution of actions. Among plants we see that 
when, instead of a imiform tissue like that of the AlgcB, 
everywhere devoted to the same process of assimilation, 
there arise, as in the Exogens, root and stem and leaves, 
there arise correspondingly unlike processes. Still more con- 
spicuously among animals, do there result varieties of function 
when the originally homogeneous mass is replaced by hetero- 


geneous organs; since both singly and by their combinations, 
do modified parts generate modified changes. Up to 

the highest organic types, this dependence continues mani- 
fest ; and it may be traced not only imder this most general 
form, but also under the more special form, that in animals 
having one set of functions developed to more than usual 
heterogeneity, there is a correspondingly heterogeneous ap- 
paratus devoted to them. Thus among birds, which have 
more varied locomotive powers than mammals, the limbs are 
more widely differentiated ; while mammals, which rise to 
more numerous and more involved adjustments of inner to 
outer relations than birds, have more complex nervous 

§ 58. It is a generalization almost equally obvious with 
the last, that functions, like structures, arise by progressive 
differentiations. Just as an organ is first an indefinite rudi- 
ment, having nothing but some most general characteristic 
in common with the form it is ultimately to take; so a 
function begins as a kind of action that is like the kind of 
action it will eventually become, only in a very vague way. 
And in functional development, as in structural development, 
the leading trait thus early manifested, is followed success- 
ively by traits of less and less importance. This holds 
equally throughout the ascending grades of organisms, and 
throughout the stages of each organism. Let us look at 
cases : confining our attention to animals, in which func- 
tional development is better displayed than in plants. 

The first differentiation established, separates the two 
fimdamentally-opposed functions above named — the accumu- 
lation of force and the expenditure of force. Passing over 
the, {Protozoa among which, however, such tribes as present 
fixed distributions of parts show us substantially the same 
thing), and commencing with the lowest Ccelenterata, where 
definite tissues make their first appearance, we observe that 
the only marked functional distinction is between the endo- 


derm, which absorbs nutriment^ and the ectoderm, which, by 
its own contractions and those of the tentacles it bears, pro- 
duces motion. That the functions of accumulation and ex- 
penditure are here very incompletely distinguished, may be 
admitted without affecting the position that this is the first 
specialization which begins to appear. These two 

most general and most radically-opposed functions, become, 
in the Polyzoa, much more clearly marked-off from each 
other ; at the same time that each of them becomes partially 
divided into subordinate functions. The endoderm and 
ectoderm are no longer merely the inner and outer walls of 
the same simple sac into which the food is drawn ; but the 
endoderm forms a true alimentary canal, separated from the 
ectoderm by a peri- visceral cavity, containing the nutritive 
matters absorbed from the food. That is to say, the function 
of accumulating force is exercised by a part distinctly divided 
from the part mainly occupied in expending force: the 
space between them, full of absorbed nutriment, effecting in 
a vague way that transfer of force which, at a higher stage of 
evolution, becomes a third leading function. Meanwhile, the 
endoderm no longer discharges the accumulative function 
in the same way throughout its whole extent ; but its differ- 
ent portions, aesophagus, stomach and intestine, perform 
different portions of this function. And instead of a con- 
tractility uniformly diffused through the ectoderm, there 
have arisen in it, some parts which have the office of con- 
tracting (muscles), and some parts which have the office of 
making them contract (nerves and ganglia). As we 

pass upwards, the transfer of force, hitherto effected quite 
incidentally, comes to have a special organ. In the ascidian 
molluscs, circulation is produced by a muscular tube, open at 
both ends, which, by a wave of contraction passing along it, 
sends out at one end the nutrient fluid drawn in at the 
other ; and which, having thus propelled the fluid for a time 
in one direction, reverses its movement and propels it in the 
opposite direction. By such means does this rudimentary 

FUNCTION. ' 159 

heart generate alternating currents in the crude and dilute 
nutriment occupying the peri-visceral cavity. How the func- 
tion of transferring force, thus vaguely indicated in these in- 
ferior forms, comes afterwards to be the definitely-separated 
office of a complicated apparatus made up of many parts, each 
of which has a particular portion of the general duty, need 
not be described. It is sufficiently manifest that this general 
function becomes more clearly marked-off from the others, 
at the same time that it becomes itself parted into subordinate 

In a developing embryo, the functions, or more strictly 
the structures which are to perform them, arise in the same 
general order. A like primary distinction very early ap- 
pears between the endoderm and the ectoderm — the part 
which has the office of accumulating force, and the part out 
of which grow those organs that are the great expenders of 
force. Between these two there presently becomes visible 
the rudiment of that vascular system, which has to fulfil the 
intermediate duty of transferring force. Of these three 
general functions, that of accumulating force is carried on 
from the outset : the endoderm, even while yet incompletely 
differentiated from the ectoderm, absorbs nutritive matters 
from the subjacent yelk. The transfer of force is also to 
some extent effected by the rudimentary vascular system, as 
soon as its central cavity and attached vessels are sketched 
out. But the expenditure of force (in the higher animals at 
least) is not appreciably displayed by the ectodermic struc- 
tures that are afterwards to be mainly devoted to. it : there 
is no sphere for the actions of these parts. Similarly 

with the chief subdivisions of these fundamental functions. 
If we look at those discharged by the ectoderm, potentially 
if not actually, we see that the distinction first established 
separates the office of transforming other force into mechani- 
cal motion, from the office of liberating the force to be so 
transformed — in the midst of the part out of which the mus- 
cular system is to be developed, there is marked-out the 


rudiment of the nervous system. This indication of struc- 
tures which are to share between them the general duty of 
expending force, is soon followed by changes that foreshadow 
further specializations of this general duty. Tn the incipient 
nervous system, there begins to arise that contrast between 
the cerebral mass and the spinal cord, which, in the main, 
answers to the division of nervous actions into directive 
and executive; and at the same time, the appearance of 
vertebral laminae foreshadows the separation of the osseous 
system, which has to resist the strains of muscular action, 
from the muscular system, which, in generating motion, en- 
tails these strains. Simultaneously there have been going 
on similar actual and potential specializations in the functions 
of accumulating force and transferring force. And through- 
out all subsequent phases, the method is substantially the 

This progress from general, indefinite, and simple kinds 
of action, to special, definite, and complex kinds of action, 
has been aptly termed by Milne-Edwards, the "physio- 
logical division of labour." Perhaps no metaphor can more 
truly express the nature of this advance from vital activity 
in its lowest forms to vital activity in its highest forms. 
And probably the general reader cannot in any other way 
obtain so clear a conception of functional development in 
organisms, as he can by tracing out functional development in 
societies : noting how there first comes a distinction between 
the governing class and the governed class ; how while in 
the governing class there slowly grow up such differences of 
duty as the civil, military, and ecclesiastical, there arise in 
the governed class, fundamentally industrial differences like 
those between agriculturists and artizans ; and how there is 
a continual multiplication of such specialized occupations, 
and specialized shares of each occupation. 

§ 59. Fully to understand this change from homogeneity 
to heterogeneity of function, which accompanies the change 



from homogeneity to heterogeneity of structure, it is needful 
to contemplate it under a converse aspect. Standing alone, 
the above exposition conveys both an inadequate and an 
erroneous idea. The divisions and subdivisions of function, 
begoming definite as they become multiplied, do not lead to 
a more and more complete independence of functions ; as 
they would do were the process nothing beyond that just de- 
scribed ; but by a simultaneous process they are rendered 
more mutually dependent. While in one respect they are 
separating from each other, they are in another respect com- 
bining with each other. At the same time that they are 
being differentiated, they are also being integrated. Some 
illustrations will make this plain. 

In animals which display little beyond the primary dif- 
ferentiation of functions, the activity of that part which 
absorbs nutriment or accumulates force, is not immediately 
bound up with the activity of that part which, in producing 
motion, e3;pend8 force. In the higher animals, however, the 
performance of the alimentary functions depends on the per- 
formance of various muscular and nervous functions. Masti- 
cation and swallowing are nervo-muscular acts; the ryth- 
mical contractions of the stomach and the allied vermicular 
motions of the intestines, result from the stimulation of cer- 
tain muscular coats by the nerve-fibres distributed through 
them ; the secretion of the several digestive fluids^ by their 
respective glands, is due to nervous excitation of them ; and 
digestion, besides requiring these special aids, is not properly 
performed in the absence of a continuous discharge of energy 
from the great nervous centres. Again, the function 

of transferring nutriment or latent force, from part to part, 
though at first not closely connected with the other functions, 
eventually becomes so. The short contractile tube which 
propels backwards and forwards the crude dilute blood con- 
tained in the perivisceral cavity of an inferior mollusc, is 
neither structurally nor functionally much entangled with 
the creature's other organs. But on passing upwards through 



the higher molluscs^ in which this simple tube is replaced 
by a system of branched tubes, that deliver their contents 
through their open ends into the tissues at distant parts; 
and on coming to those advanced types of animals which 
have closed arterial and venous systems, ramifying minutely 
in every comer of every organ ; we find that the vascular 
apparatus, while it has become structurally interwoven 
with the whole body, has become unable to fulfil its 
office without the help of offices that are quite separated from 
its own. The heart is now a complex pump, worked by 
powerful muscles that are excited by a local nervous system ; 
and the general nervous system also, takes a share in regu- 
lating the contractions both of the heart and of all the 
arteries. On the due discharge of the respiratory function, 
too, the function of circulation is directly dependent : if the 
aeration of the blood is impeded, the vascular activity is 
lowered ; and arrest of the one very soon causes stoppage of 
the other. Similarly with the duties of the nervo- 

muscular system. Animals of low organization, in which 
the differentiation and integration of the vital actions have 
not been carried far, will move about for a considerable time 
after being eviscerated, or deprived of those appliances by 
^hich force is accumulated and transferred. But animals of 
high organization are instantly killed by the removal of 
these appliances, and even by the injury of minor parts of 
them : a ^og's movements are suddenly brought to an end, by 
cutting one of the main canals along which the materials 
that evolve movements are conveyed. Thus while 

in well-developed creatures the distinction of functions is 
very marked, the combination of functions is very close. 
From instant to instant, the aeration of blood implies that 
certain respiratory muscles are being made to contract by 
certain nerves; and that the heart is duly propelling the 
blood to be aerated. From instant to instant digestion pro- 
ceeds only on condition that there is a supply of aerated blood, 
and a due current of nervous energy through the digestive 


organs. That the heart may act, it must from instant to in^ 
stant be excited by discharges from certain ganglia; and 
the discharges from these ganglia are made possible, only by 
tho conveyance to them, from instant to instant, of the 
blood which the heart propels. 

It is not easy to find an adequate expression for this double 
re-distribution of functions. It is not easy to realize a trans- 
formation through which the functions thus become in one 
sense separated and in another sense combined, or even in- 
terfused. Here, however, as before, an analogy drawn from 
social organization helps us. If we observe how the increas- 
ing division of labour in societies, is accompanied by a closer 
co-operation ; and how the agencies of different social actions, 
while becoming in one respect more distinct, become in an- 
other respect more minutely ramified through each other ; 
we shall understand better the increasing physiological co- 
operation that accompanies increasing physiological division 
of labour. Note, for example, that while local 

divisions and classes of the community have been grow- 
ing unlike in their several. occupations, the carrying on of 
their several occupations has been growing dependent on 
the due activity of that vast organization by which sus- 
tenance is collected and diffused. During the early stages 
of social development, every small group of people, and often 
every family, obtained separately its own necessaries ; but 
now, for each necessary, and for each superfluity, there ex- 
ists a combined body of wholesale and retail distributors, 
which brings its branched channels of supply within reach 
of aU. While each citizen is pursuing a business that does not 
immediately aim at the satisfaction of his personal wants, his 
personal wants are satisfied by a general agency that brings 
from all places commodities for him and his fellow-citizens 
— an agency which could not cease its special duties for a few 
days, without bringing to an end his own special duties and 
those of most others. Consider, again, how each 

of these differentiated functions is everywhere pervaded by 

11 ♦ 


certain other differentiated fonctions. Merchants, manu- 
facturers, wholesale distributors of their several species, to- 
gether with lawyers, bankers, &c., all employ clerks. In 
clerks we have a specialized class dispersed through various 
other classes ; and having its function fused with the differ- 
ent functions of these various other classes. Similarly 
commercial travellers, though having in one sense a 
separate . occupation, have in another sense an occupation 
forming part of each of the many occupations which it 
aids. As it is here with the sociological division 

of labour, so is it with the physiological division of la- 
bour above described. Just as we see in an advanced com- 
munity, that while the magisterial, the clerical, the medical, 
the legal, the manufacturing, and the commercial activities, 
have grown distinct, they have yet their agencies mingled 
together in every locality ; so in a developed organism, we 
see that while the general functions of circulation, secretion, 
absorption, excretion, contraction, excitation, &c., have be- 
come differentiated, yet through the ramifications of the sys- 
tems apportioned to them, they are closely combined with 
each other in every organ. 

§ 60. The physiological division of labour, is usually not 
carried so far as wholly to destroy the primary physiological 
community of labour. As in societies the adaptation of special 
classes to special duties, does not entirely disable these classes 
from performing each others' duties on an emergency ; so in 
organisms, tissues and structures that have become fitted to 
the particular ofiB.ces they have ordinarily to discharge, often 
remain partially able to discharge other offices. It has been 
pointed out by Dr Carpenter, that " in cases where the differ- 
ent functions are highly specialized, the general structure 
retains, more or l6s8, the primitive community of function 
which originally characterized it." A few instances will 
bring home this generalization. 

The roots and leaves of plants are widely differentia 


ated in their functions: by the roots, water and mineral 
substances are absorbed ; while the leaves take in, and de- 
compose, carbonic acid. Nevertheless, leaves retain a con- 
siderable power of absorbing water ; and in what are popu- 
larly called " air-plants," the absorption of water is wholly 
carried on by them and by the stems. Conversely, the under- 
ground parts can partially assume the functions of leaves : 
the exposed tuber of a potato develops chlorophyll on its 
surface, and in other cases, roots, properly so called, do the 
like. In trees, the trunks, which have in great measure 
ceased to produce buds^ recommence producing them if the 
branches are cut off; and imder such circumstances the 
roots, though not in the habit of developing leaf-bearing 
organs, send up numerous suckers. Much more 

various examples of vicarious function may be found among 
animals. Starting with the extreme case of the common 
hydra, which can live when the duties of skin and stomach 
have been interchanged by turning it inside out, we find in 
all grades, even up to the highest, that absorbent and excret- 
ing organs can partially supply each others' places. Among 
well-organized animals, the taking in of nutriment is ef- 
fected exclusively by an internal membrane ; but the external 
membrane is not wholly without the power to take in nutri- 
ment : when food cannot be swallowed, life may be pro- 
longed by immersing the body in nutritive fluids. The ex- 
cretion of carbonic acid and absorption of oxygen, are mainly 
performed by the lungs, in creatures which have lungs ; but 
in such creatures there continues a certain amount of cutane- 
ous respiration, and in soft-skinned batrachians like the frog, 
this cutaneous respiration is important. Again, when the 
kidneys are not discharging their duties, a notable quantity 
of urea is got rid of by perspiration. Other 

instances are supplied by the higher functions. In man, 
the limbs, which among lower vertebrates are almost wholly 
organs of locomotion, are specialized into organs of locomo- 
tion and organs of manipulation. Nevertheless, the human 


arms and legs do, when needful, fulfil, to some extent, each 
others' offices. Not only in childhood and old age are the 
arms used for purposes of support, but on occasions of emerg- 
ency, as when mountaineering, they are so used by men in full 
vigour. And that legs are to a considerable degree capable 
of performing the duties of arms, is proved by the great 
amount of manipulatory skill reached by them when the 
arms are absent. Among the perceptions, too, there are ex- 
amples of partial substitution. The deaf Dr Kitto described 
himself as having become excessively sensitive to vibrations 
propagated through the body ; and as so having gained the 
power of perceiving, through his general sensations, those 
neighbouring concussions of which the ears ordinarily give 
notice. Blind people make hearing perform, in part, the 
office of vision. Instead of identifying the positions and 
sizes of neighbouring objects by the reflection of light from 
their surfaces, they do this in a rude way by the reflection 
of sound from their surfaces. 

We see, as we might expect to see, that this power of per- 
forming more general functions, is great in proportion as 
the parts have been but little adapted to their special func- 
tions. In the hydra^ where complete transposition of functions 
is possible, the histological differentiation that has been estab- 
lished, is extremely slight, or even inappreciable. Those parts 
of plants which show so considerable a power of discharging 
each others* offices, are not widely unlike in their minute 
structures. And the tissues that in animals are to some 
extent mutually vicarious, are tissues in which the original --^^^ 
cellular composition is still conspicuous. But we do not find 
evidence that the muscular, nervous, or osseous tissues are 
able in any degree to perform those processes which the 
less differentiated tissues perform. Nor have we any 
proof that nerve can partially fulfil the duty of muscle, 
or muscle that of nerve. We must say, therefore, that 
the ability to resume the primordial community of function. 


varies inversely as the established specialization of function ; 
and that it disappears when the specialization of function 
becomes great. 

§ 61. Something approaching to a priori reasons may be 
given for the conclusions thus reached a posteriori. They 
must be accepted for as much as they seem worth. 

It may be argued that on the hypothesis of Evolution, 
Life necessarily comes before organization. On this hypo- 
thesis, organic matter in a state of homogeneous aggregation, 
must precede organic matter in a state of heterogeneous ag- 
gregation. But since the parsing from a structureless state 
to a structured state, is itself a vital process, it follows that 
vital activity must have esist^d while there was yet no 
structure : structure could not else arise. That 

function takes precedence of structure, seems also implied in 
the definition of Life. If Life consists of inner actions so 
adjusted as to balance outer actions — ^if the actions are the 
substance of Life, while the adjustment of them constitutes 
its form ; then, may we not say that the actions to be formed 
must come before that which forms them — ^that the continu- 
ous change which is the basis of function, must come before 
the structure which brings function into shape P Or 

again, since throughout all phases of Life up to the highest, 
every advance is the effecting of some better adjustment of 
inner to outer actions; and since the accompanying new com- 
plexity of structure is simply a means of making possible 
this better adjustment; it follows that function is from 
beginning to end the determining cause of structure. Not 
only is this manifestly true where the modification of struc- 
ture arises by reaction from modification of function ; but it 
is also true where a modification of structure otherwise pro- 
duced, apparently initiates a modification of function. For 
it is only when such so-called spontaneous modification of 
structure subserves some advantageous action, that it is per- 


manently established : if it is a structural modification that 
happens to facilitate the vital activities, " natural selection '' 
retains and increases it ; but if not, it disappears. 

The connexion which we noted between heterogeneity 
of structure and heterogeneity of functioo — a connexion 
made so familiar by experience as to appear scarcely worth 
specifying — is clearly a necessary one. It follows from the 
general truth that in proportion to the heterogeneity of any 
aggregate, is the heterogeneity it will produce, in. any inci- 
dent force (First Principles ^ § 116). The force continually 
liberated in the organism by decomposition, is here the inci- 
dent force ; the functions are the variously modified forms 
produced in its divisions by the organs they pass through ; 
and the more multiform the organs the more multiform must 
be the differentiations of the force passing through them. 

It follows obviously from this, that if structure progresses 
from the homogeneous, indefinite, and incoherent, to the 
heterogeneous, definite, and coherent, so too must Amotion. 
If the number of different parts in an aggregate must deter- 
mine the number of differentiations produced in the forces 
passing through it — ^if the distinctness of these parts from each 
other, must involve distinctness in their reactions, and there- 
fore distinctness between the divisions of the differentiated 
force ; there cannot but be a complete parallelism between 
the development of structure and the development of func- 
tion. If structure advances from the simple and geiieral to 
the complex and special, function must do the same. 



§ 62. Throughout the vegetal kingdom, the processes of 
Waste and Repair are comparatively insignificant in their 
amounts. Though plants, and especially certaiu parts of 
them^ do, in the absence of light or imder particular con- 
ditions, give out carbonic acid; yet this carbonic acid, 
assuming it to indicate consumption of tissue, indicates but a 
small consumption. Of course if there is little waste, there 
can be but little repair — that is, little of the interstitial repair 
which restores the integrity of parts worn by functional acti- 
vity. Nor, indeed, is there displayed by plants in any con- 
siderable degree, if at all, that other species of repair which 
consists in the restoration of lost or injured organs. Torn 
leaves and the shoots that are shortened by the pruner, do 
not reproduce their missing parts ; and though when the 
branch of a tree is cut off close to the trunk, the place is in 
the course of years covered over, it is not by any reparative 
action in the wounded surface, but by the lateral growth of 
the adjacent bark. Hence, without saying that Waste and 
Repair do not go on at all in plants, we may fitly pass them 
over as of no importance. 

There are but slight indications of waste in those lower 
orders of animals which, by their comparative inactivity, 
show themselves least removed from vegetal life. ActiniaB 
kept in an aquarium, do not appreciably diminish in bulk 


from prolonged abstinence. Even fish, though much more 
active than most other aquatic creatures, appear to undergo 
but Kttle loss of substance when kept' unfed during con- 
siderable periods. Eeptiles, too, maintaining no great 
temperature, and passing their lives mostly in a state of 
torpor, suffer but little diminution of mass by waste. When, 
however, we turn to those higher orders of animals which 
are active and hot-blooded, we see that waste is rapid: 
producing when unchecked, a notable decrease in bulk 
and weight, ending very shortly in death. Besides 

finding that waste is inconsiderable in creatures that pro- 
duce but little insensible and sensible motion, and that it 
becomes conspicuous in creatures that produce much insen- 
sible and sensible motion ; we find that in the same crea- 
tures there is most waste when most motion is generated. 
This is clearly proved by hybernating animals. " Va- 
lentin found that the waking marmot excreted in the average 
75 times more carbonic acid, and inhaled 41 times more 
oxygen than the same animal in the most complete state of 
hybernation. The stages between waking and most pro- 
found hybernation yielded intermediate figures. A waking 
hedgehog yielded about 20*5 times more carbonic acid, and 
consumed 18'4 times more oxygen than one in the state of hy- 
bernation." If we take these quantities of absorbed oxygen 
and excreted carbonic acid, as indicating something like the 
relative amounts of consumed organic substance, we see 
that there is a striking contrast between the waste ac- 
companying the ordinary state of activity, and the waste 
accompanying complete quiescence and reduced temperature. 
This difference is still more definitely shown by the fact, 
that the mean daily loss from starvation in rabbits and 
guinea-pigs, bears to that from hybernation, the proportion 
of 183 : 1. Among men and domestic animals, the relation 
between degree of waste and amount of expended force, 
though one respecting which there is little doubt, is less 
distinctly demonstrable ; since waste is not allowed to go on 


Tiniiiterfered with. We have however In the lingering lives of 
invalids who are able to take Bcarcely any nutriment, but 
are kept warm and still, an illustration of the extent to 
which waste dinunishes as the expenditure of force declines. 

Besides the connexion between the waste of the organism 
as a whole, and the production of sensible and insensible 
motion by the organism as a whole ; there is a traceable 
connexion between the waste of special parts and the activi- 
ties of such special parts. Experiments have shown that '' the 
starving pigeon daily consumes in the average 40 times 
more muscular substance than the marmot in the state of 
torpor, and only 11 times more fat, 33 times more of the 
tissue of the alimentary canal, 18*3 times 'more liver, 15 
times more lung, 5 times more skin." That is to say, in 
the hybemating animal the parts least consumed are the 
almost totally quiescent motor-organs, and the part most 
consumed is the hydro-carbonaceous deposit serving as a 
store of force ; whereas in the pigeon, similarly unsupplied 
with food but awake and active, the greatest loss takes place 
in the motor-organs. The relation between special 

activity and special waste, is illustrated too in the daily 
experiences of all : not indeed in the measurable decrease of 
the active parts in bulk or weight, for this we have no m6ans 
of ascertaining ; but in the diminished ability of such parts 
to perform their functions. That legs exerted for many hours 
in walking, and arms long strained in rowing, lose their 
powers — ^that eyes become enfeebled by reading or writing 
without intermission — ^that concentrated attention unbroken 
by rest, so prostrates the brain as to incapacitate it for think- 
ing; are familiar truths. And though we have no direct 
evidence to this effect, there is little danger in concluding that 
muscles exercised until they ache or become stiff, and nerves 
of sense rendered weary or obtuse by work, are organs so 
much wasted by action as to be partially incompetent. 

Repair is everywhere and always making up for waste. 
Though the two processes vary in their relative rates, both 


are constantly going on. Though during the active, waking 
state of an animal, waste is in excess of repair, yet repair is 
in progress ; and though during sleep, repair is in excess of 
waste, yet some waste is necessitated by the carrying on of 
certain neyer-ceasing functions. The organs of these never- 
ceasing functions furnish, indeed, the most conclusive proofs 
of the simultaneity of repair and waste. Day and night the 
heart never stops beating, but only varies in the rapidity 
and vigour of its beats ; and hence the loss of substance 
which its contractions from moment to moment entail, must 
from moment to moment be made good. Day and night 
the lungs dilate and collapse ; and the muscles which make 
them do this, must therefore be ever kept in a state of integ- 
rity by a repair which keeps pace with waste, or which 
alternately falls behind and gets in advance of it to a very 
slight extent. 

On a survey of the facts, we see, as we might expect to 
see, that repair is most rapid when activity is most reduced. 
Assiuning that the organs which absorb and circulate nutri- 
ment are in proper order, the restoration of the organism 
to a state of integrity, after the disintegration consequent 
on expenditure of force, is proportionate to the diminution 
in expenditure of force. Thus we all know that those 
who are in health, feel the greatest return of vigour after 
profound sleep — after complete cessation of motion. We 
know that a night during which the quiescence, bodily 
and mental, has been less decided, is usually not followed by 
that spontaneous overflow of energy that indicates a high 
state of efficiency throughout the organism. "We know, 
again, that long-continued recumbency, even with wakeftd- 
ness (providing the wakefulness is not the result of disorder), 
is followed by a certain renewal of strength ; though a re- 
newal less than that which would have followed the greater 
inactivity of slumber. We know, too, that when exhausted 
by labour, sitting brings a partial return of vigour. And 
we abo know that after the violent exertion of running, 


a lapse into the less violent exertion of walking, results in 
a gradual disappearance of that prostration which the run- 
ning produced. This series of illustrations conclusively 
proves that the rebuilding of the organism is ever making 
up for the pulling down of it caused by action ; and that the 
effect of this rebuilding becomes manifest, in proportion as 
the pulling down is less rapid. From each digested meal, 
there is every few hours absorbed into the mass of prepared 
nutriment circulating through the body, a fresh supply of 
the needful organic compounds ; and from the blood thus 
occasionally re-enriched, the organs through which it passes 
are ever taking up materials to replace the materials used up 
in the discharge of functions. During activity, the reinte- 
gration falls in arrear of the disintegration ; until, as a conse- 
quence, there presently comes a general state of functional 
languor ; ending, at length, in a quiescence which permits the 
reintegration to exceed the disintegration, and restore the 
parts to their state of integrity. Here, as wherever there 
are antagonistic actions, we see rhythmical divergences on 
opposite sides of the medium state— changes which equilibrate 
each other by their alternate excesses. (First Principles, 

Illustrations are not wanting of special repair, that is 
similarly ever in progress, and similarly has intervals during 
which it falls below waste and rises above it. Every one 
knows that a muscle, or a set of muscles, continuously strain- 
ed, as by holding out a weight at arm's length, soon loses its 
power ; and that it recovers its power more or less fully after 
a short rest. The several organs of special sensation yield 
us like experiences : strong tastes, powerful odours, and loud 
sounds, temporarily unfit the nerves impressed by them, for 
appreciating faint tastes, odours, or sounds ; but these inca- 
pacities are remedied by brief intervals of repose. Vision 
still better illustrates this simultaneity of waste and repair. 
Looking at the sun so affects the eye that, for a short time, 
it cannot perceive the ordinary contrasts of light and shade. 


After gazing at a bright light of a particular colour^ we see 
on turning. the eyes to adjacent objects, an image of the 
complementary colour; shotting that the retina has, for the 
moment, lost the power to feel small amounts of those rays 
which have strongly affected it. Such inabilities disappear 
in a few seconds or a few minutes, according to circumstances. 
And here, indeed, we are introduced to a conclusiye proof 
that special repair is ever neutralizing special waste. Fol* 
the rapidity with which the eyes recover their sensitiveness, 
varies with the reparative power of the individual. In youth, 
the visual apparatus is so quickly restored to its state of in- 
tegrity, that many of these photogeneSy as they are called,* 
cannot be perceived. When sitting on the far side of a room, 
and gazing out of the window against a light sky, a person 
who is debilitated by disease or advancing years, perceives, 
on transferring the gaze to the adjacent wall, a momentary 
negative image of the window — the sash-bars appearing light 
and the squares dark ; but a young and healthy person has 
no such experience. With a rich blood and vigorous circu- 
lation, the repair of the visual nerves after impressions of 
moderate intensity, is nearly instantaneous. 

Function carried to excess, may produce waste so great, 
that repair cannot make up for it during the ordinary 
daily periods of rest ; and there may result incapacities of 
the overtaxed organs, lasting for considerable periods. We 
know that eyes strained by long-continued minute work, lose 
their power for months or years : perhaps suffering an injury 
which they never wholly recover. Brains, too, are often so 
unduly worked that permanent relaxation fails to restore 
them to vigour. Even of the motor organs the like holds. 
The most frequent cause of what is called " wasting palsy,'* 
or atrophy of the muscles, is habitual excess of exertion : the 
proof, being, that the disease occurs most frequently among 
those engaged in laborious handicrafts, and usually attacks 
first the muscles that have been most worked. 

There has yet to be noticed another kind of repair ; — that 


namely, by which injured or lost parts are restored. Among 
the Hydrozoa it is common for any portion of the body to re* 
produce the rest ; even though the rest to be so reproduced 
is the greater part of the whole. In the more highly*organ-* 
ized Actinozoa, the half of an individual will grow into a 
complete individual. Some of the lower Annelids, as the 
Nais, may be cut into thirty or forty pieces, and each piece will 
eventually become a perfect animal. As we ascend to higher 
forms, we find this reparative power much diminished, though 
still considerable. The reproduction of a lost claw by a 
lobster or crab, is a familiar instance. Some of the inferior 
Vertebrata also, as lizards, can develop new limbs or new 
tails, in place of those that have been cut off; and can even 
do this several times over, though with decreasing complete- 
ness. The highest ajumals* however, thus repair themselves 
to but a very small extent. Mammals and birds do it only 
in the healing of wounds ; and very oft^n but imperfectly 
even in this. For in muscular and glandular organs, the 
tissues destroyed are not properly reproduced, but are re- 
placed by tissue of an irregular kind, which serves to hold 
the parts together. So that the power of reproducing lost parts 
is greatest where the organization is lowest ; and almost dis- 
appears where the organization is highest. And though we 
cannot say that between these extremes there is a constant in- 
verse relation between reparative power and degree of organ- 
ization; yet we may say that there is some approach to 
such a relation. 

§ 63. There is a very obvious and complete harmony be- 
tween the first of the above inductions, and the deduction 
that follows immediately from first principles. We have 
already seen (§ 23) " that whatever amoimt of power an 
organism expends in any shape, is the correlate and equi- 
valent of a power that was taken into it from without." 
Motion, sensible or insensible, generated by an organism, is 
insensible motion which was absorbed in producing certain 


chemical compounds appropriated by the organism under 
the form of food. As much power as was required to raise 
the elements of these complex atoms to their state of unsta- 
ble equilibrium, is given oat in their falls to a state of stable 
equilibrium ; and having fallen to a state of stable equilib- 
rium, they can give out no further power, but have to be 
got rid of as inert and useless. It is an inevitable corollary 
" from the persistence of force, that each portion of mechanical 
or other energy which an organism exerts, implies the trans- 
formation of as much organic matter as contained this 
energy in a latent state ; " and that this organic matter in 
yielding up its latent energy, loses its value for the purposes 
of life, and becomes waste matter needing to be excreted. 
The loss of these complex unstable substances must hence be 
proportionate to the quantity of expended force. Here then 
is the rationale of certain general facts lately indicated. 
Plants do not waste to any considerable degree, for the obvi- 
ous reason that the sensible and insensible motions they 
generate are inconsiderable. Between the small waste, small 
activity, and low temperature of the inferior animals, the rela- 
tion is similarly one admitting of a priori establishment. Con- 
versely, the rapid waste of energetic, hot-blooded animals 
might be foreseen with equal certainty. And not less mani- 
festly necessary is the variation in waste which, in the same 
organism, attends the variation in the heat and mechanical 
motion produced. 

Between the activity of a special part and the waste of 
that part, a like relation may be deductively inferred ; though 
it cannot be inferred that this relation is equally defi- 
nite. Were the activity of every organ quite independent 
of the activities of other organs, we might expect to trace 
out this relation distinctly ; but since one part of the force 
which any organ expends, is derived from materials brought 
to it by the blood from moment to moment in quantities 
varying with the demand, and since another part of the 
force which such organ expends, comes to it in the shape of 


nervous discharges from distant organs ; it is clear that spe- 
cial waste and general waste are too much entangled to 
admit of a definite relation being established between special 
waste and special activity. "We may fairly say, however, 
that this relation is quite as manifest as we can reasonably 

§ 64. Deductive interpretation of the phenomena of Re- 
pair, is by no means so easy. The tendency displayed by an 
animal organism, as well as by each of its organs, to return 
to a state of integrity by the assimilation of new matter, 
when it has undergone the waste consequent on activity, is a 
tendency which is not manifestly deducible from first princi- 
ples ; though it appears to be in harmony with them. If 
in the blood there existed ready-formed units exactly like in 
kind to those of which each organ consists, the sorting of these 
units, ending in the union of each kind with already existing 
groups of the same kind, would be merely a good example of 
Differentiation and Integration (First Principles, § 123). It 
would be analogous to the process by which, from a mixed 
solution of salts, there are deposited segregated masses of 
these salts, in the shape of different crystals. But as already 
said (§ 54), though the selective assimilation by which the 
repair of organs is effected, no doubt results in part from an 
action of this kind, which is consequent on the persistence of 
force (First Principles, § 129), the facts cannot be thus wholly 
accounted for; since organs are in part made up of units 
that do not exist as such in the circulating fluids. The pro- 
cess becomes comprehensible however, if it be shown that, as 
suggested in § 54, groups of compoimd units have a certain 
power of moulding adjacent fit materials into imits of their 
own form. Let us see whether there is not reason to think 
such a power exists. 

" The poison of small-pox or of scarlatina," remarks Mr 
Paget, " being once added to the blood, presently affects the 
composition of the whole : the disease pursues its course, 



and, if recovery ensue, the blood will seem to have returned 
to its previous condition : yet it is not as it was before ; for 
now the same poison may be added to it with impunity." 
* ♦ * "The change once effected, may be maintained 
through life. And herein seems to be a proof of the assimil- 
ative force in the blood ; for there seems no other mode of 
explaining these cases than by admitting that the altered 
particles have the power of assimilating to themselves all 
those by which they are being replaced : in other words, aU 
the blood that is formed after such a disease deviates from 
the natural composition, so far as to acquire the peculiarity 
engendered by the disease : it is formed according to the 
altered model'' Now if the compoimd molecules of the 
blood, or of an organism considered in the aggregate, have 
the power of moulding into their own type, the matters 
which they absorb as nutriment ; and if, as Mr Paget 
points out, they have the power when their type has been 
changed by disease, of moulding all materials afterwards 
received into the modified type; may we not reasonably 
suspect that the more or less specialized molecules of each 
organ, have, in like manner, the power of moulding the 
materials which the blood brings to them, into similarly 
specialized molecules P The one conclusion seems to be a 
corollary from the other. Such a power cannot be claimed 
for the component units of the blood, without being con- 
ceded to the component units of every tissue. Indeed the 
assertion of this power is little more than an assertion of the 
fact, that organs composed of specialized units are capable 
of resuming their structural integrity, after they have been 
wasted by function. For if they do this, they must do it by 
forming from the materials brought to them, certain special- 
ized units like in kind to those of which they are composed ; 
and to say that they do this, is to say that their component 
units have the power of moulding fit materials into other 
units of the same order. 

The repair of a wasted tissue may therefore be considered 


as due to forces analogous to those by whicli a crystal repro- 
duces its lost apex, when placed in a solution like that from 
which it was formed. In either case, a mass of unifjs of a 
given kind, shows a power of integrating with itself diffiised 
units of the same kind : the only difference being, that the 
organic mass of units arranges the diffused units into special 
compound forms, before integrating them with itself. In 
the case of the crystal, this reintegration is ascribed to 
polarity — a power of whose nature we know nothing. What- 
ever be its nature, however, it appears probable that the 
power by which organs repair themselves from the nutritive 
matters circulating through them, is of the same order. 

§ 65. That other kind of repair which shows itself in the 
regeneration of lost members, is comprehensible only as an 
effect of actions like those just referred to. The ability of 
an organism to recomplete itself when one of its parts has 
been cut off, is of the same order as the ability of an injured 
crystal to recomplete itself. In either case, the newly-assimi- 
lated matter is so deposited as to restore the original outline. 
And if in the case of the crystal, we say that the whole 
aggregate exerts over its parts, a force which constrains the 
newly-integrated atoms to take a certain definite form ; we 
must in the case of the organism, assume an analogous force. 
This is, in truth, not an hypothesis : it is nothing more than 
a generalized expression of the facts. If when the leg of a 
lizard has been amputated, there presently buds out the germ 
of a new one, which, passing through phases of development 
like those of the original leg, eventually assumes a like shape 
and structure ; we assert nothing more than what we see, 
when we assert that the organism as a whole exercises such 
power over the newly- fonning limb, as makes it a repetition 
of its predecessor. If a leg is reproduced where there was a 
leg, and a tail where there was a tail ; we have no alternative 
but to conclude that the aggregate forces of the body, con- 
trol the formative processes going on in each part. And on 



contemplating these facts in connexion with yarions kindred 
ones, there is suggested the hypothesis, that the form of each 
species of organism is determined by a pecuKarity in the con- 
fititution of its units — that these have a special structure in 
which they tend to arrange themselves ; just as have the 
simpler units of inorganic matter. Let us glance at the evi- 
dences which more especially thrust this conclusion upon us. 

A fragment of a Begonia-leaf, imbedded in fit soil and kept 
at an appropriate temperature, will develop a young Bego- 
nia ; and so small is the fragment which is thus capable of 
originating a complete plant, that something like a hundred 
plants might be produced from a single leaf. The friend to 
whom I owe this observation, tells me that various succulent 
plants have like powers of multiplication. Illustrating a 
similar power among animals, we have the often-cited exper- 
iments of Trembley on the common polype. Each of the 
four pieces into which one of these creatures was cut, grew 
into a perfect individual. In each of these again, bisection 
and tri-section effected a like result. And so with their 
segments, similarly produced, until as many as fifty polypes 
had resulted from the original one. Bodies when cut off 
regenerated heads ; heads regenerated bodies ; and when a 
polype had been divided into as many pieces as was practica- 
ble, nearly every piece survived and became a complete 
animal. What, now, is the implication P We 

cannot say that in each portion of a Begonia-leaf, and in 
every fragment of a Hydra's body, there exists a ready- 
formed model of the entire organism. Even were there 
warrant for the now abandoned doctrine, that the germ of 
every organism contains the perfect organism in miniature, it 
still could not be contended that each considerable part of the 
perfect organism resulting from such a germ, contains another 
such miniature. Indeed the one hypothesis obviously nega- 
tives the other. We have therefore no alternative but to 
say, that the living particles composing one of these frag- 
ments, have an innate tendency to arrange themselves into 


the shape of the organism to which they belong. We must 
infer that a plant or animal of any species, is made up of 
special units, in all of which there dwells the intrinsic apti- 
tude to aggregate into the form of that species : just as in the 
atoms of a salt, there dwells the intrinsic aptitude to crystal- 
lize in a particular way. It seems difficult to conceive that 
this can be so ; but we see that it is so. Groups of uilits 
taken from an organism (providing they are of a certain 
bulk and not much differentiated into special structures) have 
this power of re-arranging themselves ; and we are thus 
compelled to recognize the tendency to assume the specific 
form, as inherent in all parts of the organism. Mani- 

festly too, if we are thus to interpret the reproduction 
of an organism from one of its amorphous fragments, 
we must thus interpret the reproduction of any minor 
portion of an organism by the remainder. When in place 
of its lost claw, a lobster puts forth from the same spot a 
cellular mass, which, while increasing in bulk, assumes the 
form and structure of the original claw ; we can have no 
hesitation in ascribing this result to a play of forces like 
that which moulds the materials contained in a piece of 
Begonia-leaf into the shape of a young Begonia, In the one 
case as in the other, the vitalized molecules composing the 
tissues, show their proclivity towards a particular arrange- 
ment ; and whether such proclivity is exhibited in repro- 
ducing the entire form, or in completing it when rendered 
imperfect, matters not. 

For this property there is no fit term. If we accept the 
word polarity, as a name for the force by which inorganic 
units are aggregated into a form peculiar to them ; we may 
apply this word to the analogous force displayed by organic 
units. But, as above admitted, polaiity, as ascribed to atoms, 
is but a name for something of which we are ignorant — a 
name for a hjrpothetical property which as much needs ex- 
planation as that which it is used to explain. Nevertheless, 
in default of another word, we must employ this : taking 


care, however, to restrict its meaning. If we simply substi- 
tute the term polarity, for the circuitous expression — the 
power which certain units have of arranging themselves 
into a special form, we may, without assuming anything 
more than is proved, use the term organic polarity or po- 
larity of the organic units, to signify the proximate cause 
of the ability which organisms display of reproducing lost 

§ 66. As we shall have frequent occasion hereafter to refer 
to these imits, which possess the property of arranging 
themselves into the special structures of the organisms 
to which they belong ; it will be well here to ask what 
these units are, and by what name they may be most fitly 

On the one hand, it cannot be in those proximate chemical 
compounds composing organic bodies, that this specific polar- 
ity dwells. It cannot be that the atoms of albumen, or fibrine, 
or gelatine, or the hypothetical protein-substance, possess 
this power of aggregating into specific shapes ; for in 
such case, there would be nothing to account for the unlike- 
nesses of different organisms. Millions of species of plants 
and animals, more or less contrasted in their structures, 
are all mainly built up of these complex atoms. But if the 
polarities of these atoms determined the forms of the or- 
ganisms they composed, the occurrence of such endlessly 
varied forms would be inexplicable. Hence, what we may 
call the chemical units, are clearly not the possessors of this 

On the other hand, this property cannot reside in what 
may be roughly distinguished as the morphological units. The 
germ of every organism is a microscopic cell. It is by 
multiplication of cells that all the early developmental changes 
are effected. The various tissues which successively arise 
in the unfolding organism, are primarily cellular ; and in 
many of them the formation of cells continues to be, through- 


out life, the process by which repair is carried on. But 
though cells are so generally the ultimate visible components 
of organisms, that they may with some show of reason be 
called the morphological units ; yet, as they are not uni- 
versal, we cannot say that this tendency to aggregate into 
specified forms dwells in them. Finding that in many 
cases a fibrous tissue arises out of a structureless blastema, 
without cell-formation ; and finding that there are creatures, 
such as Rhizopods, which are not cellular, but nevertheless 
exhibit vital activities, and perpetuate in their progeny 
certain specific distinctions ; we are forbidden to ascribe to 
cells this peculiar power of arrangement. Nor, indeed, 
were cells universal, would such an hypothesis be acceptable ; 
since the formation of a cell is, to some extent a manifesta- 
tion of this same peculiar power. 

If, then, this organic polarity can be possessed neither by 
the chemical units nor the morphological units, we must 
conceive it as possessed by certain intermediate units, which 
we may i^rm physiological. There seems no alternative but 
to suppose, that the chemical units combine into units 
immensely more complex than themselves, complex as they 
are ; and that in each organism, the physiological units 
produced by this further compounding of highly compound 
atoms, have a more or less distinctive character. We must 
conclude that in each case, some slight difference of com- 
position in these units, leading to some slight difference in 
their mutual play of forces, produces a difference in the form 
which the aggregate of them assumes. 

The facts contained in this chapter, form but a small part 
of the evidence which thrusts this assumption upon us. We 
shall hereafter find various reasons for inferring that such 
physiological units exist, and that to their specific properties, 
more or less unlike in each plant and animal, various organic 
phenomena are due. 



§ 67. In plants, waste and repair being scarcely appre- 
ciable, there are not likely to arise appreciable changes in the 
proportions of already- formed parts. The only divergences 
from the average structure of a species, which we may expect 
particular conditions to produce, are those producible by the 
action of these conditions on parts in course of formation ; 
and such divergences we do find. We know that a tree 
which, standing alone in an exposed position, has a short 
and thick stem, has a tall and slender stem when it grows 
in a wood ; and that its branches then take a difierent inclin- 
ation. We know that potato-sprouts which, on reaching 
the light, develop into foliage, will, in the absence of 
light, grow to a length of several feet without foliage. 
And every in-door plant furnishes proof, that shoots and 
leaves, by habitually turning themselves to the light, exhibit 
a certain adaptation — an adaptation due, as we must suppose, 
to the special effects of the special conditions on the still grow- 
ing parts. In animals, however, besides analogous 
structural changes wrought during the period of growth, 
by subjection to circumstances unlike the ordinary circum- 
stances ; there are structural changes similarly wrought, 
after maturity has been reached. Organs that have 
arrived at their fiill size, possess a certain modifiability ; 
so that while the organism as a whole, retains pretty 


nearly the same bulk, the proportions of its parts may bo 
considerably varied. Their yariations, here treated of under 
the title Adaptation, depend on specialities of individual 
action. We saw in the last chapter, that the actions of or- 
ganisms entail re-actions on them ; and that specialities of 
action entail specialities of re-action. Here it remains to be 
pointed out, that the special actions and redactions do not end 
with temporary changes, but work permanent changes. 

If, in an adult animal, the waste and repair in aU parts 
were exactly balanced — ^if each organ daily gained by 
nutrition, exactly as much as it lost daily by the discharge of 
its function — ^if excess of function were followed only by such 
excess of nutrition as balanced the extra waste ; it is clear 
that there would occur no change in the relative sizes of 
organs. But there is no such exact balance. If the excess 
of function, and consequent excess of waste, is moderate, it is 
not simply compensated by repair, but more than compensated 
— ^there is a certain increase of bulk. This is true to some 
degree of the organism as a whole, when the organism is 
framed for activity, A considerable waste giving considerable 
power of assimilation, is more favourable to accumulation of 
tissue, than is quiescence with its comparatively feeble assimi- 
lation : whence results a certain adaptation of the whole 
organism to its requirements. But it is more especially true 
of the parts of an organism in relation to each other. The 
illustrations fall into several groups. The growth 

of muscles exercised to an unusual degree, is a matter of com- 
mon observation. In the often-cited blacksmith's arm, the 
dancer's legs, and the jockey's crural adductors, we have 
marked examples of a modifiability which almost every one 
has to some extent experienced. It is needless to multi- 
ply proofs. The occurrence of changes in the struc- 
ture of the skin, where the skin is exposed to a stress of 
function, is also familiar. That thickening of the epidermis 
on a labourer's palm, results from continual pressure and 
friction, is certain : those who have not before exerted their 


hands, find that such an exercise as rowings soon begins to 
produce a like thickening. This relation of cause and effect 
is stiU better shown by the marked indurations at the ends of 
a violinist's fingers. Even in mucous membrane, which 
ordinarily is not subject to mechanical forces of any intensity, 
similar modifications are possible: witness the callosity of 
the gums which arises in those who have lost their teeth, and 
have to masticate without teeth. The vascular 

system furnishes good instances of the increased growth 
that follows increased function. When, because of some 
permanent obstruction to the circulation, the heart has to 
exert a greater contractile force on the mass of blood which it 
propels at each pulsation into the arteries, and when there re- 
sults the laboured action known as palpitation ; there usually 
occurs dilatation, or hypertrophy, or a mixture of the two : 
the dilatation, which is a yielding of the heart's structure 
under the increased strain, implying a failure to meet the 
emergency ; but the hypertrophy, which consists in a thick- 
ening of the heart's muscular walls, being an adaptation of it 
to the additional effort required. Again, when an aneurism 
in some considerable artery has been obliterated, either arti- 
ficially or by a natural inflammatory process ; and when this 
artery has consequently ceased to be a channel for the blood; 
some of the adjacent arteries which anastomose with it, 
become enlarged, so as to carry the needful quantity of blood 
to the parts supplied. Though we have no direct 

proof of analogous modifications in nervous structures ; yet 
indirect proof is given by the greater eflBciency that fol- 
lows greater activity. This is manifested alike in the 
senses and the intellect. The palate may be cultivated in- 
to extreme sensitiveness, as in professional tea-tasters. An 
orchestral conductor gains by continual practice, an unusually 
great ability to discriminate differences of sound. And in 
the finger-reading of the blind, we have evidence that the 
sense of touch may be brought by exercise to a far higher 
capability than is ordinary. The increase of power which 


habitual exertion gives to mental faculties, needs no illastra- 
tion: every person of education Las personal experience 
of it. Even from the osseous structures, evidence 

may be drawn. The bones of men accustomed to great mus- 
cular action, are more massive and have more strongly 
marked processes for the attachment of muscles, than the 
bones of men who lead sedentary lives ; and a like contrast 
holds between the bones of wild and tame animals of the 
same species. Adaptations of another order, in which there 
is a qualitative rather than a quantitative modification, arise 
after certain accidents to which the skeleton is liable. When 
the hip-joint has been dislocated, and long delay has made it 
impossible to restore the parts to their proper places, the 
head of the thigh-bone, imbedded in the surrounding muscles, 
becomes fixed in its new position by attachments of fibrous 
tissue, which afford support enough to permit a halting walk. 
But the most remarkable modification of this order occurs in 
imunited fractures. "False joints'^ are often formed — 
joints which rudely simulate the hinge structure or the ball- 
and-socket structure, according as the muscles tend to pro- 
duce a motion of flexion and extension or a motion of rota- 
tion. In the one case, according to Rokitansky, the two ends 
of the broken bone become smooth and covered with perios- 
teum and fibrous tissue, and are attached by ligaments that 
allow a certain backward and forward motion; and in the 
other case, the ends, similarly clothed witL the appropriate 
membranes, become the one convex and the other concave, 
are inclosed in a capsule, and are even occasionally supplied 
with synovial fluid I 

The general truth that extra function is followed by extra 
growth, must be supplemented by the equally general truth, 
that beyond a limit, usually soon reached, very little, if any, 
further modification can be produced. The experiences from 
which we draw the one induction thrust the other upon us. 
After a time, no training makes the pugilist or the athlete 
any stronger. The adult gymnast at last acquires the power 


to perform certain difficult feats ; but certain more difficult 
feats, no additional practice enables him to perform. Years of 
discipline give the singer a particular loudness and range of 
voice, beyond which further discipline does not give greater 
loudness or wider range : on the contrary, increased vocal ex- 
ercise, causing a waste in excess of repair, is often followed 
by decrease of power. In the perceptions we see 

similar limits. The culture which exalts the susceptibility of 
the ear to the intervals and harmonies of notes, will not 
turn a bad ear into a good one. Life-long eflfort fails to 
make this artist a correct draftsman, or that a fine colourist : 
each does better than he did at first, but each falls short of 
the power attained by some other artists. Nor is 

this truth less clearly illustrated among the more complex 
mental powers. Each man has a mathematical faculty, a 
poetical faculty, or an oratorical faculty, which special educa- 
tion improves to a certain extent. But unless he is imusually 
endowed in one of these directions, no amount of education 
wiU make him a first-rate mathematician, a first-rate poet, or 
a first-rate orator. Thus the general fact appears to 

be, that while in each individual, certain changes in the 
proportions of parts, may be caused by variations of function, 
the congenital structure of each individual puts a limit to 
the modifiability of every part. Nor is this true of 

individuals only : it holds, in a sense, of species. Leaving 
open the question whether, in indefinite time, indefinite modi- 
fication may not be produced ; experience proves that within 
assigned times, the changes wrought in races of organisms 
by changes of conditions fall within narrow limits. "We see, 
for instance, that though by discipline, aided by selective 
breeding, one variety of horse has had its locomotive power 
increased considerably beyond the locomotive powers of other 
varieties ; yet that further increase takes place, if at all, at an 
inappreciable rate. The difierent kinds of dogs, too, in 
which different forms and capacities have been established, 
do not show aptitudes for diverging in the same directions at 



considerable rates. In domestic animals generally, certain 
accessions of intelligence have been produced by culture ; but 
accessions beyond these are inconspiciious. It seems that 
in each species of organism, there is a margin for functional 
oscillations on all sides of a mean state, and a consequent 
margin of structural variations ; that it is possible rapidly to 
push functional and structural changes towards the extreme 
of this margin in any direction, both in an individual and 
in a race ; but that to push these changes further in any 
direction, and so to alter the organism as to bring its mean 
state up to the extreme of the margin in that direction, is a 
comparatively slow process.* 

We have also to note that the limited increase of size pro- 
duced in any organ by a limited increase of its function, is 
not maintained unless the increase of function is permanent. 
A mature man or other animal, led by circumstances into 
exerting particular members in unusual degrees, and acquir- 
ing extra size and power in these members, begins to lose 
such extra size and power on ceasing to exert these members; 
and eventually lapses more or less nearly into the original 
state. Legs strengthened by a pedestrian tour, become weak 
again after a prolonged return to sedentary life. Tlie 
acquired ability to perform feats of skill, disappears in course 
of time, if the performance of them is given up. For compara- 
tive failure in executing a piece of music, in playing a game 
at chess, or in anything requiring special culture, the being 
out of practice is a reason of which every one recognizes the 
validity. It is observable, too, that the rapidity and com- 
pleteness with which an artificial power is lost, is proportionate 
to the shortness of the cultivation which evoked it. One who 
has for many years persevered in habits which exercise 
special muscles or special faculties of mind, retains the extra 

• Here, as in sundry places throughout this chapter, the necessities of the argu- 
ment have obliged me to forestall myself, by assuming the conclusion reached in a 
subsequent chapter, that modifications of structure produced by modifications of 
function, are transmitted to offspring. 


capacity produced, to a very considerable degree, even after a 
long period of desistance ; but one who has persevered in such 
habits for but a short time, has, at the end of a like period, 
scarcely any of the facility he had gained. Here, 

too, as before, successions of organisms present an analogous 
fact. A species in which domestication, continued through 
many generations, has organized certain peculiarities ; and 
which afterwards, escaping domestic discipline, returns to 
something like its original habits ; soon loses, in great mea- 
sure, such peculiarities. Though it is not true, as alleged, 
that it resumes completely the structure it had before domes- 
tication ; yet it approximates to that structure. The Dingo, 
or wild dog of Australia, is one of the instances given 
of this ; and the wild horse of South America is another. 
Mankind, too, supplies us with instances. In the Austra- 
lian bush, and in the backwoods of America, the Anglo- 
Saxon race, in which civilization has developed the higher 
feelings to a considerable degree, rapidly lapses into compara- 
tive barbarism : adopting the moral code, and sometimes the 
habits, of savages. 

§ 68. It is important to reach, if possible, some rationale 
of these general truths — especially of the last two. A right 
understanding of these laws of organic modification, underlies 
a right understanding of the great question of species. 
While, as before hinted (§ 40), the action of structure on 
function, is one of the factors in that process of differentiation 
by which unlike forms of plants and animals are produced, 
the re-action of function on structure, is another factor. 
Hence, it is well worth while inquiring how far these induc- 
tions are deductively interpretable. 

The first of them is the most difficult to deal with. Why 
an organ exerted somewhat beyond its wont, should presently 
grow, and thus meet increase of demand by increase of sup- 
plj^, is not obvious. We know, indeed, {First Principles, 
§§ 96, 133,) that of necessity, the rhythmical changes pro- 


duced by antagonist organic actions^ cannot any of them be 
carried to an excess in one direction, without there being 
produced an equivalent excess in the opposite direction. It 
is a corollary from the persistence of force, that any deviation 
eflfected by a disturbing cause, acting on some member of a 
moving equilibrium, must (unless it altogether destroys the 
moving equilibrium) be eventually followed by a compensating 
deviation. Hence, that excess of repair should succeed ex- 
cess of waste, is to be expected. But how happens the mean 
state of the organ to be changed P If. daily extra waste 
naturally brings about daily extra repair, only to an equiva- 
lent extent, the mean state of the organ should remain con- 
stant. How then comes the organ to augment in size and 
power P 

Such answer to this question as we may hope to find, must 
be looked for in the effects wrought on the organism as a 
whole, by increased function in one of its parts. For since 
the discharge of its function by any part, is possible only on 
condition that those various other functions on which its own 
is immediately dependent, are also discharged; it follows 
that excess in its function presupposes some excess in their 
functions. Additional work given to a muscle, implies ad- 
ditional work given to the branch arteries which bring it 
blood, and additional work, smaller in proportion, to the 
arteries from which these branch arteries come. Similarly, 
the smaller and larger veins which take away the blood, as 
well as the absorbents which carry off effete products, must 
have more to do. And yet further, on the nervous centres 
which excite the muscle, a certain extra duty must fall. But 
excess of waste will entail excess of repair, in these parts as 
well as in the muscle. The several appliances by which the 
nutrition and excitation of an organ are carried on, must also 
be influenced by this rhythm of action and re-action ; and 
therefore, after losing more than usual by the destructive 
process, they must gain more than usual by the constructive 
process. But temporarily-increased efficiency in these ap- 



pliances by which blood and nervous force are brought to an 
organ, will cause extra assimilation in the organ, beyond 
that required to balance its extra expenditure. Regarding 
the functions as constituting a moving equilibrium, we may 
say, that divergence of any function in the direction of in- 
crease, causes the functions with which it is bound up to 
diverge in the same direction ; that these again cause the 
functions which they are bound up with, also to diverge in 
the same direction ; and that these divergences of the con- 
nected functions, allow the specially-affected function to be 
carried further in this direction than it could otherwise be 
— ^further than the perturbing force could carry it if it had a 
fixed basis. 

It must be admitted that this is but a vague explanation. 
Among actions so involved as these, we can scarcely expect 
to do more than dimly discern a harmony with first princi- 
ples. That the facts are to be interpreted in some such way, 
may, however, be inferred from the circumstance that an 
extra supply of blood continues for some time to be sent to 
an organ that has been imusually exercised ; and that when 
unusual exercise is long continued, a permanent increase of 
vascularity results. 

§ 69. Answers to the questions — Why do these adaptive 
modifications in an individual animal, soon reach a limit? 
and why, in the descendants of such animal, similarly condi- 
tioned, is this limit very slowly extended P — are to be found 
in the same direction as was the answer to the last question. 
And here the connexion of cause and consequence is much 
more manifest. 

Since the function of any organ is dependent on the fimc- 
tions of the organs which supply it with materials and forces ; 
and since the functions of these subsidiary organs are de- 
pendent on the functions of organs which supply them with 
materials and forces ; it follows that before any great extra 
power of discharging its function, can be gained by a 


specially-exercised organ, a considerable extra power must 
be gained by a series of immediately-subservient organs, and 
some extra power by a secondary series of remotely-sub- 
servient organs. Thus there are required numerous and 
wide-spread modifications. Before the artery which feeds a 
hard-worked muscle, can permanently furnish a large ad- 
ditional quantity of blood, it must increase in diameter and 
contractile power ; and that its increase of diameter and con- 
tractile power may be of use, the main artery from which it 
diverges, must also be so far modified as to bring this addi- 
tional quantity of blood to the branch artery. Similarly 
with the veins ; similarly with the absorbents ; similarly 
with the nerves. And when we ask what these subsidiary 
changes imply, we are forced to conclude that there must be 
an analogous group of more numerous changes, ramifying 
throughout the system. The growth of the arteries prima- 
rily and secondarily implicated, cannot go to any extent, 
without growth in the minor blood-vessels on which their 
nutrition depends ; while their greater contractile power in- 
volves enlargement of the nerves which excite them, and 
some modification of that part of the spinal cord whence 
these nerves proceed. Thus, without tracing the like remote 
alterations implied by extra growth of the veins, absorbents, 
and other agencies, it is manifest that a large amount of re- 
building must be done throughout the organism, before any 
organ of importance can be permanently increased in size 
and power to a great extent. Hence, though such extra 
growth in any part as does not necessitate considerable 
changes throughout the rest of the organism, may rapidly 
take place ; a further growth in this part, requiring a re- 
modelling of numerous parts remotely and slightly afiected, 
must take place but slowly. 

We have before found our conceptions of vital processes 
made clearer by studying analogous social processes. In 
societies there is a mutual dependence of functions, essentially 
like that which exists in organisms; and there is also an 



essentially like re-action of Amotions on structures. From the 
laws of adaptive modification in societies^ we may therefore 
hope to get a clue to the laws of adaptive modification in 
organisms. Let us suppose, then, that a society has arrived 
at a state of equilibrium like that of a mature animal — a 
state not like our own, in which growth and structural de- 
velopment are rapidly going on; but a state of settled 
balance among the j^ctional powers of the various classes 
and industrial bodies, and a consequent fixity in the relative 
sizes of such classes and bodies. Further, let us suppose 
that in a society thus balanced, there occurs something which 
throws an imusual demand on some one industry — say an 
imusual demand for ships (which we will assume to be built 
of iron) in consequence of a competing mercantile nation 
having been prostrated by famine or pestilence. The imme- 
diate result of this additional demand for iron ships, is the 
employment of more workmen, and the purchase of more iron, 
by the ship-builders ; and when, presently, the demand con- 
tinuing, the builders find their premises and machinery in- 
suj£cient, they enlarge them. If the extra requirement 
persists, the high interest and high wages bring such extra 
capital and labour into the business, as are needed for new 
ship-building establishments. But such extra capital and 
labour do not come quickly ; since, in a balanced community, 
not increasing in population and wealth, labour and capital 
have to be drawn from other industries, where they are 
already yielding the ordinary returns. Let us now go a 
step further. Suppose that this iron-ship-building industry, 
having enlarged as much as the available capital and labour 
permit, is still unequal to the demand ; what limits its im- 
mediate further growth ? The lack of iron. By the hypo- 
thesis, the iron-producing industry, like all the other indus- 
tries throughout the community, yields only as much iron as 
is habitually required for all the purposes to which iron is 
applied : ship-building being only one. If, then, extra iron 
is required for ship-j^uilding, the first efiect is to withdraw 


part of the iron habitually consumed for other purposes, and 
to raise the price of iron. Presently, the iron-makers feel 
this change, and their stocks dwindle. As, however, the 
quantity of iron required for ship-building, forms but a smaU 
part of the total quantity required for all purposes ; the ex- 
tra demand on the iron-makers, can be nothing liklB so great 
in proportion as is the extra demand on the ship-builders. 
Whence it follows, that there will be much less tendency to 
an immediate enlargement of the iron-producing industry — 
the extra quantity will for some time be obtained by working 
extra hours. Nevertheless, if, as fast as more iron can be 
thus supplied, the ship-building industry goes on growing 
— if, consequently, the iron-makers experience a permanently- 
increased demand, and out of their greater profits get higher 
interest on capital, as well as pay higher wages ; there will 
eventually be an abstraction of capital and labour from other 
industries, to enlarge the iron- producing industry : new blast- 
furnaces, new rolling-mills, new cottages for workmen, will 
be erected. But obviously, the inertia of capital and labour 
to be overcome, before the iron-producing industry can grow 
by a decrease of some other industries, will prevent its growth 
from taking place until long after the increased ship-build- 
ing industry has demanded it ; and meanwhile, the growth 
of the ship-building industry must be limited by the 
deficiency of iron. A remoter restraint of the same nature, 
meets us if we go a step further — a restraint which can 
be overcome, only in a still longer time. For the manu- 
facture of iron depends on the supply of coal. The pro- 
duction of coal being previously in equilibrium with the 
consumption ; and the consumption of coal for the manu- 
facture of iron, being but a small part of the total con- 
sumption ; it follows that a considerable extension of the iron 
manufacture, when it at length takes place, will cause but a 
comparatively small additional demand on the coal-owners and 
coal-miners— a demand which will not, for a long period, suf- 
fice to cause enlargement of the coal- trade, by drawing capital 


and labour from other investments and occupations. And 
until the permanent extra demand for coal, has become great 
enough to draw from other investments and occupations, suf- 
ficient capital and labour to sink new mines, the increasing 
production of iron must be restricted by the scarcity of coal ; 
and the multiplication of ship-yards and ship-builders, 
must be checked by the want of iron. Thus, in a com- 
mimity which has reached a state of moving equilibrium, 
though any one industry directly affected by an additional 
demand, may rapidly imdergo a small extra growth; 
yet a growth beyond this, requiring, as it does, the build- 
ing-up of subservient industries, less directly and strongly 
affected, as well as the partial t^wbuilding of other industries, 
can take place only with comparative slowness. And a 
still further growth, requiring structural modifications of 
industries still more distantly affected, must take place .still 
more slowly. 

E/Ctuming from this analogy, we realize more clearly the 
truth, that any considerable member of an animal organism, 
cannot be greatly enlarged without some general re-organiza- 
tion. Besides a building-up of the primary, secondary, and 
tertiary groups of subservient parts, there must be an un- 
building of sundry non-subservient parts ; — or at any rate, 
there must be permanently established, a lower nutrition of 
such non-subservient parts. For it must be remembered that 
in a mature animal, or one which has reached a balance 
between assimilation and expenditure, there cannot be an in- 
crease in the nutrition of some organs, without a decrease in 
the nutrition of others ; and an organic establishment of the 
increase, implies an organic establishment of the decrease — 
implies more or less change in the processes and structures 
throughout the entire system. And here, in- 

deed, is disclosed one reason why growing animals under- 
go adaptations so much more readily than adult ones. For 
while there is surplus nutrition, it is possible for specially-ex- 
ercised parts to be specially enlarged, without any. positive 


deduction from other parts. There is required only that 
negative deduction, shown in the diminished growth of other 

§ 70. Pursuing the argument farther, we reach an ex- 
planation of the third general truth ; namely, that organisms, 
and species of organisms, which, under new conditions, have 
undergone adaptive modifications, soon return to something 
like their original structures, when restored to their original 
conditions. Seeing, as we have done, how excess of action 
and excess of nutrition in any part of an organism, must 
affect action and nutrition in subservient parts, and 
these again in other parts, until the re-action has divided 
and subdivided itself throughout the organism, affecting 
in decreasing degrees the more and more numerous parts 
more and more remotely implicated ; we see that the 
consequent changes in the parts remotely implicated, consti- 
tuting the great mass of the organism, must be extremely 
slow. Hence, if the need for the adaptive modification 
ceases, before the great mass of the organism has been much 
altered in its structure by these ramified but minute re-ac- 
tions; we shall have a condition in which the specially- 
modified part, is not in equilibrium with the rest. All the 
remotely-affected organs, as yet but little changed, will, in the 
absence of the perturbing cause, resume very nearly their 
previous actions. The parts that depend on them, will 
consequently by and by do the same. Until at length, by a 
reversal of the adaptive process, the organ at first affected will 
be brought back almost to its original state. Eecon- 

sidering the above-drawn analogy between an organism and 
society, will enable us better to realize this necessity. If, in 
the case supposed, the extra demand for iron ships, after 
causing the erection of some additional ship-yards and the 
drawing of iron from other manufactures, were to cease ; 
the old dimensions of the ship-building trade would be 
quickly returned to : discharged workmen would seek fresh 


occupations, and the new yards would be devoted to other 
uses. But if the increased need for ships lasted long 
enough, and became great enough, to cause a flow of capital 
and labour from other industries into the iron-manufacture, a 
falling off in the demand for ships, would much less rapidly 
entail a dwindling of the ship-building industry. For iron 
being now produced in greater quantity, a diminished con- 
sumption of it for ships, would cause a fall in its price, and 
a consequent fall iu the cost of ships: thus enabling the 
ship-builders to meet the competition which we may sup- 
pose led to a decrease in the orders they received. And since, 
when new blast-furnaces and rolling-mills, &c., had been built 
with capital drawn from other industries, its transference 
back into other industries, would involve great loss ; the 
owners, rather than transfer it, would accept unusually low in- 
terest ; and an excess of iron would continue to be produced ; 
resulting in an undue cheapness of ships, and a maintenance 
of the ship-building industry at a size beyond the need. 
Eventually, however, if the number of ships required still 
diminished^ the production of iron in excess would become 
very unremunerative : some of the blast-furnaces would be 
blown out ; and as much of the capital and labour as remained 
available, would be re-distributed among other occupations. 
Without repeating the steps of the argument, it will be clear 
that were the enlargement of the ship-building industry 
great enough, and did it last long enough, to cause an in- 
crease in the number of coal-mines ; the ship-building in- 
dustry would be still better able to maintain itself under 
adverse circumstances ; but that it would, though at a more 
distant period, end by sinking down to the needful dimensions. 
Thus our conclusions are : — ^First, that if the extra activity 
and growth of a particular industry, has lasted long enough 
only to remodel the proximately-affected industries ; it will 
dwindle away again after a moderate period, if the need for 
it disappears. Second, that an enormous period must be re- 
quired before the re-actions produced by an enlarged industry, 


can cause a re-construction of the whole society, and before 
the countless re-distributions of capital and labour, can again 
reach a state of equilibrium. And third, that only when 
such a new state of equilibrium is eventually reached, can the 
adaptive modification become a permanent one. How, 

in animal organisms, the like argument will hold, needs not 
be pointed out. The reader will readily follow the parallel. 
That organic types should be comparatively stable, might 
be anticipated on the hypothesis of Evolution. If we assume, 
as we must according to this hypothesis, that the structure 
of any organism is a product of the almost infinite series of 
actions and re-actions to which all ancestral organisms have 
been exposed ; we shall see that any unusual actions and re- 
actions brought to bear on an individual, can have but 
an infinitesimal eflFect in permanently changing the structure 
of the organism as a whole. The new set of forces, com- 
pounded with all the antecedent sets of forces, can but inap- 
preciably modify that moving equilibrium of functions which 
all these antecedent sets of forces have established. Though 
there may result a considerable perturbation of certain func- 
tions — a considerable divergence from their ordinary rhythms; 
yet the general centre of equilibrium cannot be sensibly 
changed. On the removal of the perturbing cause, the pre- 
vious balance will be quickly restored : the effect of the new 
forces being almost obliterated by the enormous aggregate of 
forces which the previous balance expresses. 

§ 71. As thus understood, the phenomena of adaptation 
fall into harmony with first principles. The inference that 
organic types are fixed, because the deviations from them 
which can be produced within assignable periods, are relatively 
small ; and because, when a force producing deviation ceases, 
there is a return to something like the original state ; proves to 
be an invalid inference. Without assuming fixity of species, 
we find good reasons for anticipating that kind and degree of 
stability which is observed. We find grounds for concluding. 


a priori, that an adaptive change of structure, will soon reach 
a point beyond which further adaptation will be slow ; for 
concluding that when the modifying cause has been but 
a short time in action, the modification generated, will be 
evanescent ; for concluding that a modifying cause acting 
even for many generations, will do but little towards per- 
manently altering the organic equilibrium of a race ; 
and for concluding that on the cessations of such cause, its 
effects will become unapparent in the course of a few gener- 



§ 72. What is an individual P is a question wfiich many 
readers will think it easy to answer. Yet it is a question 
that has led to much controversy among Zoologists and 
Botanists ; and no quite satisfactory reply to it seems possi- 
ble. As applied to a man, or to any one of the higher 
animals, which are all sharply-defined and independent, the 
word individual has a clear meaniog ; though even here^ 
when we turn from average cases to exceptional cases — 
as a calf with two heads and two pairs of fore-limbs — we 
find ourselves in doubt whether to predicate one individuality 
or two. But when we extend our range of observation to 
the organic world at large, we find that difiiculties allied to 
this exceptional one, meet us everywhere under every variety 
of form. 

Each uniaxial plant may perhaps fairly be regarded as a 
distinct individual ; though there are botanists who do not 
make even this admission. What, however, are we to say of 
a multiaxial plant P It is, indeed, usual to speak of a tree 
with its many branches and shoots, as singular ; but strong 
reasons may be urged for considering it as plural. Every 
one of its axes has a more or less independent life, and when 
cut off and planted, may grow into the likeness of its parent; 
or by grafting and budding, parts of this tree may be 
developed upon another tree, and there manifest their 


speciiic peculiarities. Shall we regard all the growing axes 
thus resulting from slips and grafts and buds, as parts of one 
individual, or as distinct individuals ? If a strawberry- plant 
sends out runners carrying buds at their ends/ which strike 
root and grow into independent plants, that separate from 
the original one by decay of the runners, must we not say 
that they possess separate individualities ; and yet if we do 
this, are we not at a loss to say when their separate individu- 
alities were established, unless we admit that each bud was 
from the beginning an individual ? Commenting on such 
perplexities, Schleiden says — " Much has been written and 
disputed concerning the conception of the individual, with- 
out, however, elucidating the subject, principally owing to 
the misconception that still exists as to the origin of the con- 
ception. Now the individual is no conception, but the mere 
subjective comprehension of an actual object, presented to us 
under some given specific conception, and •on this latter it 
alone depends whether the object is or is not an individual. 
Under the specific conception of the solar system, ours is an 
individual : in relation to the specific conception of a planet- 
ary body, it is an aggregate of many individuals." ♦ ♦ * " I 
think, however, that looking at the indubitable facts 
already mentioned, and the relations treated of in the course of 
these considerations, it will appear most advantageous and 
most useful, in a scientific point of view, to consider the 
vegetable cell as the general type of the plant (simple plant 
of the first order). Tinder this conception, Protococcua and 
other plants consisting of only one cell, and the spore and 
poUen-granule, will appear as individuals. Such individuals 
may, however, again, with a partial renunciation of their in- 
dividual independence, combine under definite laws into 
definite forms (somewhat as the individual animals do in the 
globe of the Volvox globator*). These again appear empiri- 
cally as individual beings, under a conception of a species 

• It is now generally agreed that the Volvox globator is a plant. 


(simple plants of the second order) derived from the form of 
the normal connexion of the elementary individuals. But 
we cannot stop here, since nature herself combines these in- 
dividuals, under a definite form, into larger associations^ 
whence we draw the third conception of the plant, from a 
connexion, as it were, of the second power (compound plants 
— plants of the third order). The simple plant proceeding 
from the combination of the elementary individuals is then 
termed a bud {gemma) ^ in the composition of plants of the 
third order." 

The animal kingdom presents still greater difficulties. 
When, from sundry points on the body of a oonmion polype, 
there bud-out young polypes, which, after acquiring mouths 
and tentacles and closing up the communications between 
their stomachs and the stomach of the parent, finally separate 
from the parent ; we may with propriety regard them as dis- 
tinct individuals. But when, in the allied compound Hydro^ 
zoa, we find that these young polypes continue permanently 
connected with the parent ; and when, by this continuous 
budding-out, there is presently produced a tree-like aggre- 
gation, having a common alimentary canal into which the 
digestive cavity of each polype opens; it is no longer so 
clear that these little sacs furnished with mouths and tenta- 
cles, are severally to be regarded as distinct individuals. We 
cannot deny a certain individuality to the polypedom. And 
on discovering that some of the buds, instead of unfolding in 
the same manner as the rest, are transformed into capsules 
in which eggs are developed— on discovering that certain of 
the incipient polypes thus become wholly dependent on the 
^■ggregate for their nutrition, and discharge functions which 
have nothing to do with their own maintenance, we have 
still clearer proof that the individualities of the members are 
partially merged in the individuality of the group. Other 
organisms belonging to the same order, display still more 
decidedly this transition from simple individualities to a com- 
plex individuality. In the Diphyes there is a special modifi- 


cation of one or more members of the polypedom into a 
swimming apparatus, which, by its rhythmical contractions, 
propels itself through the water, drawiug the polypedom after 
it. And in the more differentiated Physalia, various organs 
result from the metamorphosis of parts that are the homo- 
logues of individual polypes. In this last instance, the in- 
dividuality of the aggregate is so predominant, that the 
individualities of the members are practically lost. This 

combination of individualities in such way as to produce a 
composite individual, meets us in other forms among the 
ascidian molluscs. While in some of these, as in the 
Clavelina, the animals associated are but little subordinated 
to the community they form ; in others, as in the Botry Hides, 
they are so fused into a rounded mass, as to present the 
appearance of a single animal with several mouths and 

On the hypothesis of Evolution, perplexities of this nature 
are just such as we might anticipate. If Life in general, com- 
menced with minute and simple forms, like those out of 
which all individual organisms, however complex, now 
originate ; and if the transitions from these primordial imits 
to organisms made up of groups of such units, and to higher 
organisms made up of groups of such groups, took place by 
degrees; it is clear that individualities of the first and 
simplest order, would merge gradually in those of a larger 
and more complex order, and these again in others of an 
order having still greater bulk and organization ; and that 
hence it would be impossible to say where the lower indivi- 
dualities ceased, and the higher individualities commenced. 

§ 73. To meet these difficulties, it has been proposed that 
the whole product of a single fertilized germ, shall be re- 
garded as a single individual : whether such whole product 
be organized into one mass, or whether it be organized into 
many masses, that are partially or completely separate. It 
is urged that whether the development of the fertilized germ 


be continuous or discontinuous (§ 50) is a matter of secondary 
importance ; that the totality of living tissue to which the 
fertilized germ gives rise in any one case, is the equivalent 
of the totality to which it gives rise in any other case ; and 
that we must recognize this equivalence, whether such totality 
of living tissue takes a concrete or a discrete arrangement. 
In pursuance of this view, a zoological individual is consti- 
tuted either by any such single animal as a mammal or bird, 
which may properly claim tlie title of a zoon, or by any such 
group of animals as the numerous Medusce that have been 
developed from the same egg, which are to be severally dis- 
tinguished as zooids. 

Admitting it to be very desirable that there should be 
words for expressing these relations and this equivalence, it 
may still be objected, that to apply the word individual to a 
number of separate living bodies, is inconvenient : conflictingso 
much, as it does, with the ordinary conception which this word 
suggests. It seems a questionable use of language to say that 
the countless masses of Anacharis Alsinastrum, which, within 
these few years, have grown up in our rivers, canals, and 
ponds, are all parts of one individual ; and yet as this plant 
does not seed in England, these countless masses, having 
arisen by discontinuous development, must be so regarded, if 
we accept the above definition. 

It may be contended, too, that while it does violence to 
our established way of thinking, this mode of interpreting 
the facts is not without its difficulties — smaller, perhaps, 
than those it escapes, but still considerable. Something 
seems to be gained by restricting the application of the title 
individual, to organisms which, being in all respects fuUy 
developed, possess the power of producing their kind after 
the ordinary sexual method; and denying this title to those 
incomplete organisms which have not this power. But the 
definition does not really establish this distinction for us. On 
the one hand, we have cases in which, as in the working bee, 
the whole of the germ-product is aggregated into a single 


organism ; and yet, though, an indiyidual according to the 
definition, this organism has no power of reproducing its 
kind. On the other hand, we have cases like that of the 
perfect Aphides^ where the organism is but an infinitesimal 
part of the germ-product ; and yet has that completeness 
required for sexual reproduction. Moreover, if we 

adopt the proposed view, we find ourselves committed to the 
anomalous position, that among many orders of animals, there 
are no concrete individuals at all. If the individual is consti- 
tuted by the whole germ-product, whether continuously or 
discontinuously developed, then, not only must individuality 
be denied to each of the imperfect Aphides^ but also to 
each of the perfect males and females; since no one of 
them is more than a minute fraction of the total germ- 
product. And yet fiirther, it might be urged with 
some show of reason, that if the conception of individuality 
involves the conception of completeness ; then, an organism 
which possesses an independent power of reproducing itself, 
being more complete than an organism in which this power 
is dependent on the aid of another organism, is more in- 

§ 74. There is, indeed, as already implied, no definition 
of individuality that is unobjectionable. All we can do is to 
make the best practicable compromise. 

As applied either to an animate or an inanimate object, 
the word individual ordinarily connotes union among -the 
parts of the object, and separateness from other objects. 
This fundamental element in the conception of indi^'iduality, 
we cannot with propriety ignore in the biological application 
of the word. That which we call an individual plant or animal, 
must, therefore, be some concrete whole, and not a discrete 
whole. If, however, we say that each concrete 

living whole is to be regarded as an individual, we are still 
met by the question — What constitutes a concrete living 
whole ? A young organism arising by internal or external 


gemmation from a parent organism, passes gradually from a 
state in which it is an indistinguishable part of the parent 
organism, to a state in which it is a separate organism of like 
structure with the parent. At what stage does it become an 
individual P And if its individuality be conceded only when 
it completely separates from the parent, must we deny in- 
dividuality to all organisms thus produced, which permanently 
retain their connexions with their parents P Or again, what 
must we say of the Hectoeotylus, which is an arm of the 
Cuttle-fish that undergoes a special development, and then 
detaching itself, lives independently for a considerable 
period P And what must we say of that larval Echinus, 
which is left to move about awhile after being robbed of its 
viscera by the young Echinus developed within it P 

To answer such questions, we must revert to the definition 
of Life. The distinction between individual in its biological 
sense, and individual in its more general sense, must consist 
in the manifestation of Life, properly so called. Life we 
have seen to be, ** the definite combination of heterogeneous 
changes, both simultaneous and successive, in correspondence 
with external co-existences and sequences." Hence, a biolo- 
gical individual is any concrete whole having a structure 
which enables it, when placed in appropriate conditions, to 
continuously adjust its internal relations to external relations, 
so as to maintain the equilibrium of its functions. In 

pursuance of this conception, we must consider as individuals, 
all those wholly or partially independent organized masses, 
which arise by multicentral and multiaxial development that 
is either continuous or discontinuous (§ 60). We must 
accord the title to each separate aphis, each polype of a 
polypedom, each bud or shoot of a flowering plant, whether 
it detaches itself as a bulbil or remains attached as a branch. 

By thus interpreting the facts, we do not, indeed, avoid all 
anomalies. While, among flowering plants, the power of in- 
dependent growth and development, is usually possessed only 
by shoots or axes ; yet, in some casee, as in that of the Begonia- 


leaf awhile since mentioned, the appendage 6f an axis, or even 
a small fragment of such appendage, is capable of initiating 
and carrying on the functions of life ; and in other cases, as 
shown by M. Naudin in the Drosera intermedia^ young 
plants are occasionally developed from the surfaces of leaves, 
while still connected with the parent plant. Nor among 
forms like the compound Hydrozoa^ does the definition 
enable us to decide where the line is to be drawn between 
the individuality of the group and the individualities of the 
members — ^merging into each other, as these do, in different 
degrees. But, as before said, such difficulties must necessa- 
rily present themselves, if organic forms have arisen by in- 
sensible gradations. We must be content with a course 
which commits us to the smallest number of incongruities ; 
and this course is, to consider as an individual, any centre or 
axis that is capable of independently carrying on that con- 
tinuous adjustment of inner to outer relations which consti- 
tutes Life. 



§ 76. Having concluded what constitutes an individual, 
we are in a position to deal with the multiplication of in- 
dividuals. For this, the title Genesis is here chosen, as being 
the most comprehensive title — the least specialized in its 
meaning. By some biologists, Generation has been used to 
signify one method of multiplication, and Reproduction to 
signify another method ; and each of these words has been 
thus rendered in some degree unfit to signify multiplication 
in general. 

Here the reader is indirectly introduced to the fact, that 
the production of new organisms is carried on in fimdament- 
ally unlike ways. Up to quite recent times, it was believed, 
even by naturalists, that all the various processes of multipli- 
cation observable in different kinds of organisms, have one 
essential character in common : it was supposed that in every 
species, the successive generations are alike. It has now been 
proved, however, that in plants, and in numerous animals, the 
successive generations are not alike ; that from one generation 
there proceeds another whose members differ more or less 
in structure from their parents ; that these produce others 
like themselves, or like their parents, or like neither ; but 
that eventually, the original form re- appears. Instead of 
there being, as in the cases most familiar to us, a constant 
recurrence of the same form, there is a cyclical recurrence of 



the same form. These two distinct processes of multiplication, 
maybe aptly termed homogenesia and heterogenesis.* Under 
these heads let us consider them more closely. 

The kind of genesis, once supposed to be universal, in 
which the successive generations are alike, is always sexual 
genesis ; or, as it has been otherwise coMei—gamogenesia. In 
every species of organism which multiplies by homogenesis, 
each generation consists of males and females ; and from the 
fertilized germs they produce, the next generation of similar 
males and females arises. This method of propagation is 
further distinguished by the peculiarity, that each fertilized 
germ gives rise to but one individual — the product of de- 
velopment is always organized round one axis, and not round 
several axes. Between the different kinds of homo- 

genesis, the most marked contrast, and the only one which 
need here detain us, is that between the oviparous and the 
viviparous. The oviparous kind is that in which the fertil- 
ized germ is detached from the parent, before it has 
undergone any considerable development. The viviparous 
kind is that in which development is considerably advanced, 
or almost completed, before final detachment takes place. 
This distinction is, however, not a sharply-defined one : there 
are transitions between the oviparous and the viviparous 
processes. In ovo-viviparous genesis, there is an internal 
incubation ; and though the young are in this case finally 
detached from the parent in the shape of eggs, they do not 
leave the parent's body until after they have assumed 
something like the parental form. Looking 

around, we find that homogenesis is universal among the 
Vertehrata : there is no known vertebrate animal but what 
arises from a fertilized germ, and unites into its single indi- 
viduality the whole products of this fertilized germ. In 

♦ Unfortunately the word heterogenesis, has been already used as a synonyme 
for ** spontaneous generation." Save by those few who belieye in " spontaneous 
generation," however, little objection will be felt to using the word in a sense 
that seems much more appropriate. 

GENESIS. ' 211 

the mammals or highest Vertebrata, this homogenesis is in 
every case viviparous ; in birds it is uniformly oviparous ; 
and in reptiles and fishes, it is always essentially oviparous, 
though there are cases, of the kind above referred to, in 
which viviparity is simulated. Passing to the Invertebrata^ 
we find oviparous homogenesis universal among the Arach" 
nida (except the Scorpions, which are ovo- viviparous) ; 
universal among the higher Crustacea, but not among 
the lower ; extremely general, though not universal, among 
Insects ; and universal among the higher Mollusca, though 
not among the lower. Along with extreme inferiority among 
animals, we find homogenesis to be the exception rather 
than the rule ; and in the vegetal kingdom, there appear to 
be no cases, save those of a few aberrant parasites like the 
RaJflesiacecBy in which the centre or axis which arises from a 
fertilized germ, becomes the immediate producer of fertilized 

Where propagation is carried on by heterogenesis, or is 
characterized by unlikeness of the successive generations, 
there is always asexual genesis with occasionally-recurring 
sexual genesis; in other words — agamogenesis interrupted 
more or less frequently by gamogenesis. If we set out with 
a generation of perfect males and females ; then, from their 
ova or seeds, there arise individuals that are neither males 
nor females, but that produce the next generation from 
buds. By this method of multiplication, many individuals 
originate from a single fertilized germ: the product of 
development is organized round more than one centre or 
axis. The simplest form of heterogenesis is that 

seen in uniaxial plants. If, as we find ourselves obliged to 
do, we regard each separate shoot or axis of growth, as a dis- 
tinct individual ; then, in uniaxial plants, the successive in- 
dividuals are not represented by the series A, A, A, A, &c., 
like those resulting from homogenesis ; but they are repre- 
sented by the series A, B, A, B, A, B, &c. For in plants 
which were before classed as uniaxial (§ 50), and which may 

14 * 


be conveniently so distinguished from other plants, the axis 
which shoots up from the seed, and substantially constitutes 
the plant, does not itself flower and bear seed ; but gives lateral 
origin to flowering, or seed -bearing, axes. Though in uni- 
axial plants, the fructifying apparatus appears to be at the end 
of the primary, vertical axis; yet dissection shows that, 
morphologically considered, each fructifying axis is usually 
an offispring from the primary axis. There arises from the seed, 
a sexless individual, from which spring by gemmation, in- 
dividuals having reproductive organs ; and from these there 
result fertilized germs or seeds^ that give rise to sexless 
individuals. That is to say, gamogenesis and agamogenesis 
alternate : the peculiarity being, that the sexual individu- 
als arise from the sexless ones by continuous development. 
The Salpce show us an allied form of heterogenesis in 
the animal kingdom. Individuals developed from fertilized 
ova, instead of themselves producing fertilized ova, produce, 
by gemmation, strings of individuals ; from which fertiKzed 
ova again originate. In multiaxial plants, we have 

a succession of generations represented by the series A, B, 
B, B, &c.. A, B, B, B, &c. Supposing A to be a flowering 
axis, or sexual individual ; then, from any fertilized germ it 
casts off*, there grows up a sexless individual, B ; from this 
there bud-out other sexless individuals, B ; and so on for 
generations more or less numerous ; until at length, from 
some of these sexless individuals, there bud-out seed-bearing 
individuals of the original form A. Branched herbs, 
shrubs, and trees, exhibit this form of heterogenesis : the 
successive generations of sexless individuals thus produced, 
being in most cases continuously developed, or aggregated 
into a compound individual ; but being in some cases dis- 
continuously developed. Among animals, a kind of hetero- 
genesis represented by the same succession of letters, occurs 
in such compound polypes as the Sertularia; and in 
those of the Hydrozoa which assume alternately the poly- 
poid form, and the form of the Medusa : the chief differences 


presented by these groups, arising from the fact that the 
successive generations of sexless individuals produced by 
budding, are in some cases continuously developed, and in 

I others discontinuously developed ; and from the fact that, in 

' some cases, the sexual individuals give off their fertilized 

germs while still growing on the parent-polypedom, but in 
other cases, not until after leaving the parent-polypedom and 
undergoing further development. Where, as in all 

the foregoing kinds of agamogenesis, the new individuals 
bud-out, not from any specialized reproductive organs, but 

. from unspecialized parts of the parent ; the process has been 

named, by Prof. Owen, metagenesis. In most instances, the 
individuals thus produced, grow from the outsides of the 
parents— the metagenesis is external. But there is also a 
kind of metagenesis which we may distinguish as internal. 
Certain m^osoa of the* genus Distoma,. exhihit it. From the 

• egg of a Distoma, there results a rudely-formed creature 

known to naturalists as the " King's-yellow worm." Gradu- 
ally as this increases in size, the greater part of its inner 
V substance is transformed into young animals called Cercarim 
(which are the larvae of Distomata) ; until at length, it 
becomes little more than a living sac, full of living offspring. 
In the Distoma pacijica, the brood of young animals thus 
arising by internal gemmation, are not Cercarice, but are of 
the same form as their parent : themselves becoming the 

f producers of Cercarice after the same manner, at a subsequent 

period. So that sometimes the succession of forms is repre- 
sented by the series A, B, A, B, &c. ; and sometimes by the 
series A, B, B, A, B, B, &c. Both cases, however, exemplify 
internal metagenesis, in contrast with the several kinds of 
external metagenesis described above. That agamo- 

genesis which is carried on in a reproductive organ — either 
a true ovarium or the homologue of one — has been called, by 
Prof. Owen, parthenogenesis. In his work published under 
this title, he embraced those cases in which the buds arising 
in the pseud-ovarium, are not ova in the full sense of the 


word ; but rather, as they have since been called by Prof. 
Huxley, pseud-ova. Von Siebold and other naturalists, have 
hence applied the term parthenogenesis to a narrower class 
of cases. Perhaps it would be best to distinguish this 
process, which is intermediate between metagenesis and 
parthenogenesis, by the term pseudo-parthenogenesis. It 
is the process familiarly exemplified in the Aphides, 
Here, from the fertilized eggs laid by perfect females, there 
grow up imperfect females, in the pseud-ovaria of which 
there are developed pseud-ova ; and these, rapidly assuming 
the organization of other imperfect females, are bom vivi- 
parously. From this second generation of imperfect females, 
there by and by arises, in the same manner, a third genera- 
tion, of the same kind ; and so on for many generations : the 
series being thus symbolized by the letters A, B, B, B, B, 
B, &c., A. Bespecting this kind of heterogenesis, it should 
be added, that in animals, as in plants, the number of genera- 
tions of sexless individuals produced before the re-appearance 
of sexual ones, is indefinite ; both in the sense that in the 
same species it may go on to a greater or less extent accord- 
ing to circumstances, and in the sense that among the genera- 
tions of individuals proceeding from the same fertilized germ, 
a recurrence of sexual individuals takes place earlier in some 
of the diverging lines of multiplication than in others. In 
trees we see that on some branches, flower-bearing axes arise 
while other branches are still producing only leaf-bearing 
axes ; and in the successive generations of Aphides, a parallel 
truth has been observed. Lastly has to be set down, 

that form of heterogenesis in which, along with gamogenesis, 
there occurs a form of agamogenesis exactly like it, save in the 
absence of fecundation. This is called true parthenogenesis — 
reproduction carried on by virgin mothers, which are in all 
respects like other mothers. In the silk-worm-moths 
this parthenogenesis is exceptional, rather than ordinary : 
usually the eggs of these insects are fertilized ; but if they 
are not, they are still laid, and some of them produce larvae. 
In certain L^ndoplera, however, of the groups Psychidce and 



Tineidce, parthenogenesis appears to be a normal process — 
indeed, so far as is known, the only process ; for of some 
species the males have never been found. 

A general conception of the relations among the different 
modes of Genesis, thus briefly described, will be best given 
by the following tabular statement. 

Genesis is ^ 

HomogenesiSj which is Gamogenesis . 




. Heterogenesis, which is 



or r Internal 

. Metagenesis < or 


This, like all other classifications of such phenomena, pre- 
sents anomalies. It may be justly objected, that the processes 
here grouped under the head agamogenesis, are the same as 
those before grouped under the head of discontinuous develop- 
ment (§ 50) : thus making development and genesis partially 
coincident. Doubtless it seems awkward that what are from 
one point of view considered as structural changes, are from 
another point of view considered as modes of multiplication.* 

* Prof. Huxley avoids this difficulty by making every kind of Genesis a mode 
of development. His classification, which suggested the one given above^ is as 
follows : — 




( Metamorphosis 



There is, however, nothing for us but a choice of imperfec- 
tions. We cannot by any logical dichotomies, accurately 
express relations which, in Nature, graduate into each other 
insensibly. Neither the above, nor any other scheme, can do 
more than give an approximate idea of the truth. 

§ 76. Genesis under every form, is a process of negative 
or positive disintegration ; and is thus essentially opposed to 
that process of integration, which is one element of individual 
evolution. Negative disintegration occurs in those cases 
where, as among the compound Hydrozoay there is a con- 
tinuous development of new individuals by budding from the 
bodies of older individuals ; and where the older individuals 
are thus prevented from growing to a greater size, or reach- 
ing a higher degree of integration. Positive disintegration 
occurs in those cases of agamogenesis where the formation 
of new individuals is discontinuous, and in all cases of gamo- 
genesis. The degrees of disintegration are various. At 
the one extreme, the parent organism is completely broken 
up, or dissolved into new individuals ; and at the other 
extreme, the new individual forms but a small deduction 
from the parent organism. Protozoa and Protophyta, show 
us that form of disintegration called spontaneous fission: 
two or four individuals being produced by the splitting-up 
of the original one. The Vblvox and the Hydrodictyon, 
are plants which, having developed broods of young plants 
within themselves, give them exit by bursting ; and among 
animals, the one lately referred to, which arises from the 
Distoma egg, entirely loses its individuality in the individ- 
ualities of the numerous. Distoma-loirveQ with which it be- 
comes filled. Speaking generally, the degree of 
disintegration becomes less marked, as we approach the higher 
organic forms. Plants of advanced types throw off from 
themselves, whether by gamogenesis or agamogenesis, parts 
that are relatively small; and among the higher animals, 
there is no case in which the parent individuality is habitually 


lost, in the production of new individualities/ To the 

last, however, there is of necessity a greater pr less disinte- 
gration. The seeds and pollen-grains of a flowering plant, 
are disintegrated portions of tissue ; as are also the ova and 
spermatozoa of animals. And whether the fertilized germs 
carry away from their parents small or large quantities of 
nutriment, these quantities of nutriment in all cases involve 
further negative or positive disintegrations of the parents. 

New individuals that result from agamogenesis, usually do 
not separate from the parent-individuals, until they have 
undergone considerable development, if not complete develop- 
ment. The agamogenetic offspring of those lowest organisms 
which develop centrally, do not, of course, pass beyond cen- 
tral structure ; but the agamogenetic offspring of organisms 
that develop axially, commonly assume an axial structure 
before they become independent. The vegetal kingdom shows 
us this in the advanced organization of detached bulbils, and 
of buds that root themselves before separating. Of animals, 
the Hydrozoay the Trematoda, the Salpce, and the Aphides, 
present us with different kinds of agamogenesis, in all of 
which the new individuals are organized to a considerable 
extent before being cast off. This rule is not without excep- 
tions, however. The winter-eggs of the Plumatella, developed 
in an unspecialized part of the body, present us with a case 
of metagenesis, in which centres of development, instead of 
axes, are detached ; and in the above-described parthenogene- 
sis of moths and bees, such centres are detached from an 

When produced by gamogenesis, the new individuals be- 
come independent of the parents while in the shape of centres 
of development, rather than axes of development ; and this 
even where the reverse is apparently the case. The fertilized 
germs of those inferior plants which are central, or multicen- 
tral, in their development, are of course thrown off as centres. 
In the higher plants, of the two elements that go to the form- 
ation of the fertilized germ, the poUen-ceU is absolutely 


separated from the parent-plant under the shape of a centre ; 
and the embryo-cell, though not absolutely separated from 
the parent, is still no longer subordinate to the organizing 
forces of the parent. So that when, the embryo-cell having 
been fertilized by matter from the pollen-tube, the develop- 
ment commences, it proceeds without parental control : 
the new individual, though remaining physically united 
with the old individual, becomes structurally and functionally 
separate while still only a centre of development ; and takes 
on its axial form by processes of its own — the old individual 
doing no more than supply materials. Through- 

out the animal kingdom, the new individuals produced by 
gamogenesis, are obviously separated in the shape of centres 
of development wherever the reproduction is oviparous : the 
only conspicuous variation being in the quantity of nutritive 
matter bequeathed by the parent to the new centre of de- 
velopment, at the time of its separation. And though, where 
the reproduction is viviparous, the process appears to be 
different, and in one sense is so ; yet, intrinsically, it is the 
same. For in these cases, the new individual really detaches 
itself from the parent while still only a centre of develop- 
ment ; but instead of being finally cast off in this state, it is 
re-attached, and supplied with nutriment until it assumes a 
more or less complete axial structure. 

§ 77. Under all its various forms, the essential act in gamo- 
genesis, is the union of two centres or cells, produced by 
different parent organisms : the sperm -cell being the male 
product, and the germ-cell the female. There are very 
many modes and modifications of modes in which these 
cells are produced ; very many modes and modifications of 
modes by which they are brought into contact ; and very 
many modes and modifications of modes by which the result- 
ing fertilized germs have secured to them the fit* conditions 
for their development. But passing over these many diver- 
gent and re-divergent kinds of sexual multiplication, which 


it would take too much space here to specify, the one uni- 
versal peculiarity which it concerns us to remark, is, this co- 
alescence of a detached portion of one organism, with a more 
or less detached portion of another. 

Such protophytes as the PalmellcB and the Destnidtew, 
which are sometimes distinguished as unicellular plants, show 
us a coalescence, jiot of detached portions of two organisms, 
but of two entire organisms : in the Palmelke, conjugation is 
a complete fusion of the individuals ; and in the DesmidiecB^ 
the entire contents of the individuals unite to form the germ- 
mass. Where, as among the ConfervcBy we have aggregated 
cells whose individualities are scarcely at all subordinate to 
that of the aggregate, the gamogenetic act is effected by the 
union of the contained granules of two adjacent cells. In 
Spirogyra^ it is not adjacent cells in the same thread which 
thus combine ; but cells of one thread with those of another. 
As we ascend to] plants of high organization, we find that 
the two reproductive elements become quite distinct in 
their characters]; and further, that they arise in different 
organs set apart for their production : the arrangements 
being such, that the sperm-cells of one plant combine with 
the germ-cells of another. 

There is reason to think that, among the lowest Protozoa^ 
a fusion of two individualities, analogous to that which occurs 
in the conjugation of certain Algce, is the process from which 
results the germ of a new series of individuals. But in 
animals formed by the aggregation of units that are homolo- 
gous with Protozoa^ the sperm-cells and germ-cells are differ- 
entiated. And even in these humble forms, where there is no 
differentiation of sexes, we have good evidence that, as in all 
higher forms, the union is not between sperm-cells and germ- 
cells that have arisen in the same individual ; but between 
those that have arisen in different individuals. 

The marvellous phenomena initiated by the meeting of 
sperm-cell and germ-cell, naturally suggest the conception of 
some quite special and peculiar properties possessed by these 


cells. It seems obvious that this mysterious power which 
they display, of originating a new and complex organism, 
distinguishes them in the broadest way from portions of organic 
substance in general. Nevertheless, the more we study the 
evidence, the more is this assumption shaken — ^the more are 
we led towards the conclusion, that these cells have not 
been made by some unusual elaboration, fundamentally 
different from all other cells. The first fact which 

points to this modified conclusion, is the fact recently dwelt 
upon (§ 68), that in many plants and inferior animals, a 
small fragment of tis8.ue that is but little differentiated, is 
capable of developing into the form of the organism from 
which it was taken. Conclusive proof obliged us to admit, 
that the component units of organisms, have inherent powers 
of arranging themselves into the forms of the organisms to 
which' they belong. And if to these component units, which 
we distinguished as physiological, such powers must be con- 
ceded — ^if, under fit conditions, and when not much specialized, 
they manifest such powers in a way as marked as that in 
which the contents of sperm-cells and germ-cells manifest 
them ; then, it becomes clear that the properties of sperm- 
cells and germ-cells are not so peculiar as we are apt to 
assume. Again, the organs for preparing sperm- 

cells and germ-cells, have none of the speciality of struc- 
ture which might be looked for, did sperm-cells and germ- 
cells need endowing with properties essentially unlike 
those of all other organic agents. On the contrary, these 
reproductive centres proceed from tissues that are character- 
ized by their low organization. In plants, for example, it is 
not appendages that have acquired considerable structure, 
which produce the fructifying particles : these arise at the 
extremities of the axes, where the degree of structure is the 
least. The embryo-cells are formed in the undifferentiated 
part of the cambium-layer ; the pollen-grains are formed at 
the little-differentiated extremities of the stamens ; and both 
are homologous with simple epithelium-cells. Among many 


inferior animals devoid of speoial reproductive organs, such 
as the Hydra, the ova and spermatozoa originate in the 
layer of indifferent tissue that lies between the endoderm 
and the ectoderm ; that is, they consist of portions of the 
least specialized substance. And in the higher animals, 
these same generative agents appear to be merely modified 
epithelium-cells — cells not remarkable for their complexity 
of structure, but rather for their simplicity. If, by 

way of demurrer to this view, it is asked why other epithe- 
lium-cells do not exhibit like properties ; there are two replies. 
The first is, that other epithelium-cells are usually so far 
changed to fit them to their special fimctions, that they are 
unfitted for assuming the reproductive function. The second 
reply is, that in some cases, where the epithelium-cells are 
but very little specialized, they flfo exhibit the like properties: 
not, indeed, by imiting with other epithelium-cells to produce 
new germs, but by producing new germs without such \mion. 
I learn from Dr Hooker, that the Begonia phyllomaniaca 
habitually develops young plants from the scales of its stem 
and leaves — ^nay, that many young plants are developed by a 
single scale. The epithelium-cells composing one of these 
scales, swell, here and there, into large globular cells ; form 
chlorophyll in their interiors ; shoot out rudimentary axes ; 
and then, by spontaneous constrictions, cut themselves off; 
drop to the ground; and grow into Begonias. It appears, 
too, that in a succulent English plant, the Malaxis paludosa^ 
a like process occurs : the self-detached cells being, in this 
case, produced by the surfaces of the leaves. Thus, 

there is no warrant for the assumption that sperm-cells and 
germ-cells possess powers fundamentally unlike those of 
other cells. The inference to which the facts point, is, that 
they differ from the rest, mainly in not having undergone 
modifications such as those by which the rest are adapted to 
particular functions. They are cells that have departed but 
-little from the original and most general type. Or, in the 
words suggested by a friend, it is not that they are peculiarly 


specialized, but rather that they are unspecialized : such 
specializations as some of them exhibit in the shape of loco- 
motive appliances^ &c., being interpretable not as intrinsic, 
but as extrinsic, modifications, that have reference to nothing 
beyond certain mechanical requirements. Sundry 

facts tend likewise to show, that there does not exist the pro- 
found distinction which we are apt to assume, between the 
male and female reproductive elements. In the common 
polype, sperm-cells and germ-cells are developed in the same 
layer of indifferent tissue ; and in Tethya^ one of the sponges. 
Prof. Huxley has observed that they occur mingled together 
in the general parenchyma. The pollen-grains and embryo- 
cells of plants, arise in adjacent parts of the cambium-layer ; 
and from a description of a monstrosity in the Passion-flower, 
recently given by Mr Salter to the Linnaean Society, it ap- 
pears, both that ovules may, in their general structure, 
graduate into anthers, and that they may produce pollen in 
their interiors. All which evidence is in perfect harmony 
with the foregoing conclusion; since, if sperm-cells and 
germ-cells have natures not essentially imlike those of un- 
specialized cells in general, their natures cannot be essen- 
tially unlike ea<5h other. 

The next general fact to be noted, is, that these cells 
whose union constitutes the essential act of gamogenesis, are 
cells in which the developmental changes have come to a 
close — cells which, however favourably circumstanced in 
respect of nutrition, are incapable of further evolution. 
Though they are not, as many cells are, unfitted for growth 
and metamorphosis by being highly specialized; yet they 
have lost the power of growth and metamorphosis. They 
have severally reached a state of equilibrium. And while 
the internal balance of forces prevents a continuance of con- 
structive changes, it is readily overthrown by external 
destructive forces. For it uniformly happens that sperm- 
cells and germ-cells which are not brought in contact, disap- 
pear. In a plant, the embryo-cell, if not fertilized, is 


absorbed or dissipated, while the ovule aborts ; and the un- 
impregnated ovum eventually decomposes. 

Such being the characters of these cells, and such being 
their fates if kept apart, we have now to observe what hap- 
pens when they are united. For a long time, the immediate 
sequence of their contact was not ascertained. This is at 
length, however, decided. It has been shown that in plants, 
the extremity of the elongated pollen-cell applies itself to the 
surface of the embryo-sac, but does not enter the embryo- 
sac. In animals, however, the process is different. Careful 
observers agree, that the spermatozoon passes through the 
limiting membrane of the ovum. The result in both cases is 
presumed to be a mixture of the contents of the two 
cells. The evidence goes to show that in plants, matter 
passes by osmose from the pollen-cell into the embryo- 
cell; and that in animals, the substance contained in the 
spermatozoon becomes mingled with the substance contained 
in the ovum, either by simple diffusion or by cell-multiplica- 
tion. But the important fact which it chiefly con- 
cerns us to notice, is, that on the union of these reproductive 
elements, there begins, either at once or on the return of 
favourable conditions, a new series of developmental changes. 
The state of equilibrium at which each of them had arrived, 
is destroyed by their mutual influence ; and the constructive 
changes which had come to a close, recommence : a process 
of cell-multiplication is set up ; and the resulting cells pre- 
sently begin to aggregate into the rudiment of a new 

Thus, passing over the variable concomitants of gamo- 
genesis, and confining our attention to what is constant in it, 
we see : — ^that.there is habitually, if not universally, a fusion 
of two portions of organic substance, which are either them- 
selves distinct individuals, or are throvra off by distinct 
individuals ; that these portions of organic substance, which 
are severally distinguished by their low degree of special- 
ization, have arrived at states of structural quiescence or 


eqmlibrium ; that if they are not united, this eqinlibrium 
ends in dissolution ; but that by the mixture of them, this 
equiKbrium is destroyed, and a new evolution initiated. 

§ 78. What are the conditions under which Genesis takes 
place P How does it happen that some organisms multiply 
by homogenesis, and others by heterogenesis ? Why is it 
that where agamogenesis prevails, it is usually from time to 
time interrupted by gamogenesis? These are questions of 
extreme interest; but questions to which decisive answers 
cannot yet be g^ven. In the existing state of Biology, we 
must be content if we can learn the direction in which 
answers lie. A survey of the facts, discloses certain correla- 
tions which, if not universal, are too general to be without 

Where the multiplication of individuals is carried on by 
heterogenesis, we find, in numerous cases, that agamogenesis 
continues as long as the forces which result in growth, are 
greatly in excess of the antagonistic forces. While conversely, 
we find that the recurrence of gamogenesis, takes place when 
"the conditions are no longer so favourable to growth. In 
like maimer, where there is homogenetic multiplication, new 
individuals are usually not formed while the preceding in- 
dividuals are still rapidly growing — that is, while the forces 
producing growth exceed the opposing forces to a great extent; 
but the formation of new individuals begins when nutrition 
is nearly equalled by expenditure. To specify all the facts 
that seem to warrant these inductions, would take more, space 
than can be here spared. A few of them must suffice. 

The relation between fructification and innutrition, among 
plants, was long ago asserted by a German biologist — by 
Wolfif, I am told. When, some years ago, I met with the 
assertion, I was not acquainted with the evidence on which it 
rested. Since that time, however, I have,, when occasion 
favoured, examined into the facts for myself. The result has 
been a conviction, strengthened by every further inquiry, 


that such a rektion exists. TTniaxial plants begin to 

produce their lateral, flowering axes, only after the main 
axis has developed the great mass of its leaves, and is show- 
ing its diminished nutrition by smaller leaves, or shorter 
intemodes, or both. In multiaxial plants, two, three, or 
more generations of leaf-bearing axes, or sexless individuals, 
are prodi;ced before any seed-bearing individuals show them- 
selves. When, after this first stage of rapid growth and 
agamogenetic multiplication, some gamogenetic individuals 
arise, they do so where the nutrition is least ; — not on the 
main axis, or on the secondary axes, or even on the tertiary 
axes; but on axes that are the most removed from the 
channels which supply nutriment. Again, a flowering axis 
is commonly less bulky than the others : either much 
shorter, or, if long, much thinner. And further, it is an 
axis of which the terminal internodes are undeveloped: the 
foliar organs, which instead of becoming leaves become sepals, 
and petals, and stamens, follow each other in close succession, 
instead of being separated by portions of the still-growing 
axis. Another group of evidences meets us, when 

we observe the variations of fruit-bearing that accompany 
variations of nutrition, in the plant regarded as a whole. 
Besides finding, as above, that gamogenesis commences only 
when the luxuriance of early growth has been somewhat 
checked, by the extension of the remoter parts of the plant to 
some distance from the roots ; we find that gamogenesis is 
induced at an earlier stage than usual, by checking the nutri- 
tion. Trees are made to fruit while still quite small, by 
cutting their roots, or putting them in pots ; and luxuriant 
branches which have had the flow of sap into them diminished, 
by* what gardeners call "ringing," begin to produce flower- 
shoots instead of leaf-shoots. Moreover, it is to be remarked 
that trees which, by flowering early in the year, seem to 
show a direct relation between gamogenesis and increasing 
nutrition, really do the reverse ; for in such trees, the flower- 
buds are formed in the autumn — ^that structure which deter- 



mines these buds into sexual individuals, is given when the 
nutrition is declining. Conversely, very high nutri- 

tion in plants, prevents, or arrests, gamogenesis. It is 
notorious that unusual richness of soil, or too large a 
quantity of manure, results in a continuous production of 
leaf-bearing, or sexless, shoots. Besides being prevented 
from producing sexual individuals, by excessive nutrition, 
plants are, by excessive nutrition, made to change the sexual 
individuals they were about to produce, into sexless ones. 
This arrest of gamogenesis may be seen in various stages. 
The familiar instance of flowers made barren by the trans- 
formation of their stamens into petals, shows us the lowest 
degree of this reversed metamorphosis. Where the petals 
and stamens are partially changed into green leaves, the 
return from the gamogenetic structure towards the agamo- 
genetic structure, is more marked; and it is still more 
marked when, as occasionally happens in luxuriantly-growing 
plants, new flowering axes, and even leaf-bearing axes, grow 
out of the centres of flowers.* The anatomical 

* Among yariow examples of this whicli I hare obsenred, some of the most 
roBiarkable were among Foxgloyes, growing in great numbers and of large size, 
in a wood between Whatstandwell Bridge and Grich, in Derbyshire. In one case, 
the lowest flower on the stem, contained, in place of a pistil, a shoot or spike of 
flower-bads, similar in strnctnre to the embryo-buds of the main spike. I 
counted seventeen buds on it ; of whieh the first had three stamens, but was other- 
wise normal; the second had three; the third, four; the fourth, four; &c. 
Another plant, haying more yaried monstrosities, eyinced excess of nutrition with 
equal clearness. The following are the notes I took of its structure : — 1st, or 
lowest flower on the stem, very large; calyx containing eight divisions, one 
partly transformed into a corolla, and another transformed into a small bud with 
bract (this bud consisted of a fiye-cleft calyx, four sessile anthers, a pistil, and a 
rudimentary corolla) ; the corolla of the main flower, which was complete, con- 
tained six stamens, three of them bearing anthers, two x)thers being flattened and 
coloured, and one rudimentary ; there was no pistil, but, in place of it, a large 
hud, consisting of a three-cleft calyx, of which two divisions were tinted at the 
ends, an imperfect corolla, marked internally with the usual purple spots and 
hair8,2three anthers sessile on this mal-formed corolla, a pistil, a seed-vessel with 
ovules, and, growing to it, another bud of which the structure was indistinct. 
2nd flower, large ; calyx of seven divisions, one being transformed into a bud 


structure of the sexual axis, affords corroborative evidence : 
giving very much the impression, as it does, of an aborted 
sexless axis. Besides lacking those intemodes which the 
leaf-bearing axis commonly possesses, the flowering axis 
differs by the absence of rudimentary lateral axes. In a leaf- 
bearing axis, the axil of every leaf usually contains a small 
bud, which mAy or may not develop into a lateral axis; 
but though the petals of a flower are homologous with leaves, 
they do not bear homologous buds at their bases. Ordinarily, 
too, the foliar appendages of sexual axes, are much smaller 
than those of sexless ones — the stamens and pistils especially, 
which are the last formed, being extremely dwarfed ; and 
there is even reason for thinking that the absence of chloro- 
phyll from the parts of fructification, is a fact of like mean- 
ing. Moreover, the formation of the seed-vessel appears 
to be a direct consequence of arrested nutrition. If a 
gloved-finger be taken to represent a growing shoot, 
(the finger standing for the core of the shoot, and the 
glove for the cambium-layer, in which the process of 
growth takes place) ; and if it be supposed that there is a 
diminished supply of material for growth ; then, it seems 
a fair inference, that growth will first cease at the apex of 
the cambium-layer, represented by the end of the glove- 
finger; and supposing growth to continue in those parts 
of the cambium-layer that are nearer to the supply of nutri- 
ment, their further longitudinal extension will lead to the 
formation of a cavity at the extremity of the shoot, like that 
which results in a glove-finger when the finger is partially 
withdrawn and the glove sticks to its end. Whence it seems, 

with bract, but much smaller than the other ; corolla large but cleft along the top ; 
six stamens with anthers, pistil, and seed-yessel. 3rd flower, large; six-cleft 
calyx, cleft coroUa, with six stamens, pistil, and seed-vessel, with a second pistil 
halt unfolded at its apex. 4th flower, large ; divided along; the top, six stamens. 
5th flower, large; corolla divided into three parts, six stamens. 6th flower, 
large ; corolla cleft, calyx six -cleft, the rest of the flower normal. 7th, and all suc- 
ceeding flowers, normal. 

1-5 ♦ 


both that this introversion of the cambium-layer may be 
considered as due to failing nutrition^ and that the ovules 
growing from its introverted surface (which would have been 
its outer surface but for the defective nutrition) are extremely 
aborted homologues of external appendages — either leaves 
or lateral axes : the essential organs of fructification thus 
arising where the defective nutrition has reached its extreme.* 
To all which let us not forget to add, that the sperm- cells and 
germ-ceUs are formed at the very ends of the organs of fruc- 

Those kinds of animals which multiply by heterogenesis, 
present us with a parallel relation between the recurrence of 
gamogenesis and the recurrence of conditions unfavourable to 
growth — at least, this is shown where experiments have 
thrown light on the connexion of cause and effect ; 
namely, among the Aphides. These creatures, hatched from 
eggs in the spring, multiply by agamogenesis throughout 
the summer. When the weather becomes cold, and plants 
no longer afford abundant sap, perfect males and females 
are produced ; and from gamogenesis there result fertilized 
ova. But now observe that beyond this evidence, we 
have much more conclusive evidence. For it has been shown* 
both that the rapidity of the agamogenesis is proportionate 
to the warmth and nutrition^ and that if the temperature and 

* It appears that botanists do not agree respecting the homologies of the 
oToles: some thinking that they are rudimentary foliar organs, and others that 
they are rudimentary axial organs. Possibly the dispute will prove a bootless 
one ; since there seems evidence that ovules may be transformed into either one 
or the other. Mr Salter's paper, lately referred to, shows that they may 
graduate into stamens, which are foliar organs ; and the case of the Foxglove, 
which I have described above, shows that they may develop into flower-buds, 
which are axial organs. I would venture to suggest, that the conflicting evidence 
can be reconciled, only by regarding ovules as the homologues of lateral append- 
ages ; and considering a lateral appendage as composed of a leaf, plus a rudiment- 
ary axis, either of which may abort. This is the view which seems countenanced 
by development ; since, in its first stage, a lateral bud, whence a lateral append- 
age arises, shows no division into rudimentary leaf and rudimentary axis ; and 
it is to the lateral bud in this first stage, that the seed-bud or ovule is homo- 

'^ GENESIS. 229 

supply of food be artificially maintained, the agamogenesis 
continues through the winter. Nay more — ^it not only, under 
these conditions, continues through one winter, but it has 
been known to continue for four successive years: some 
forty or fifty sexless generations being thus produced. And 
those who have investigated the matter, see no reason to 
doubt the indefinite continuance of this agamogenetic mul- 
tiplication, so long as the external requirements are duly 
met. * Evidence of another kind, which points very 

distinctly to the same conclusion, is furnished by the hetero- 
genesis of the Daphnia — ^a small crustacean commonly known 
as the Water-flea, which inhabits ponds and ditches. From 
the nature of its habitat, this little creature is exposed to very 
variable conditions. Besides being frozen up in winter, the 
small bodies of water in which it lives, are often unduly 
heated by the summer sun, or dried up by continued drought. 
The circumstances favourable to the Daphnia'a life and 
growth, being thus liable to interruptions which, in our cli- 
mate, have a regular irregularity of recurrence ; we may, in 
conformity with the h3rpothe8is, expect to find both that the 
gamogenesis recurs along with evidence of declining nutri- 
tion, and that its recurrence is very variable. This we do 
find. From Mr Lubbock's paper on the Daphnia in the 
"Philosophical Transactions" for 1857, and from further 
information which he has been good enough to furnish me, 
the following general facts are deducible : — First, that in 
each ovarium, along with the rudiments of agamic eggs, or 
eggs which, if developed, produce young by true partheno- 
genesis, there usually, if not always, exists the rudiment of 
an ephippial egg ; which, from sundry evidences, is inferred 
to be a sexual or gamio egg. . Second, that according to cir- 
cumstances, either agamogenesis or gamogenesis takes place ; 
but that if the agamic eggs develop, the rudimentary gamic 
egg disappears, or becomes absorbed ; and conversely, if the 
gamic egg develops, the agamic eggs disappear, or are ab- 
sorbed by it. Third, that the brood of agamic eggs contained 


in each ovarium, amounts, mider favourable circumstances, 
to as many as eight or nine ; while of the gamic eggs, only 
one at a time is produced in each ovarium, and occasionally 
one of the ovaria produces none : whence it follows, that as 
the gamic egg is not more than twice the bulk of the agamic 
egg, the quantity of matter contained in an agamic brood, is 
four times, and occasionally even eight times, as great as 
that contained in a gamic brood. Thus the quantity of 
nutriment expended in gamogenesis during a given period 
(making allowance for that which goes to the formation of 
the ephippium), is far less than that expended in agamogenesis 
during a like period. Seeing, then, this constant preparation 
for either gamic or agamic genesis, in a creature liable to 
such irregular variations of nutrition ; and seeing that the 
agamogenesis implies by its amoimt, a large excess of nutri- 
tion, while the gamogenesis implies by its amount, a small 
excess of nutrition ; we can scarcely doubt that the one or 
the other mode of multiplication occurs, according as the 
external conditions, are or are not favourable to nutrition. 

Passing now to animals which multiply by homogenesis — 
animals in which the whole product of a fertilized germ ag- 
gregates round a single centre or axis, instead of round many 
centres or axes ; we see, as before, that so long as the con- 
ditions allow rapid increase in the mass of this germ-product, 
the formation of new individuals by gamogenesis does not 
take place. Speaking generally, we find that only when 
growth is declining in relative rapidity, do perfect sperm- 
cells and germ-cells begin to appear; and that the fullest 
activity of the reproductive function, arises as growth ceases 
— speaking generally, we must say, because, though this 
relation is tolerably definite in the highest orders of animals 
which multiply by gamogenesis, it is less definite in the lower 
orders. This admission does not militate against the hypo- 
thesis, as it seems to do ; for the indefiniteness of the relation 
occurs where the limit of growth is comparatively indefinite. 
We saw (§ 46) that amoiig active, hot-blooded creatures, 


such as mammals and birds, the ineyitable balancing of 
assimilation by expenditure, establishes, for each species, an 
almost uniform adult size ; and among creatures of these 
kinds, (birds especially, in which this restrictive effect of 
expenditure is most conspicuous), the connexion between 
cessation of growth and commencement of reproduction, is 
distinct. But we also saw (§ 46) that where, as in the Cro- 
codile and the Pike, the conditions and habits of life are such, 
that expenditure does not overtake assimilation as the size 
increases, there is no precise limit of growth ; and in creatures 
thus circumstanced, we may naturally look for a compara- 
tively indeterminate relation between declining growth and 
commencing reproduction.* There is, indeed, among 

fishes, at least one case which appears very anomalous. The 
male parr, or young of the male salmon, a fish of four or five 
inches in length, is said to produce milt% Having, at this 
early stage of its growth, not one hundredth of the weight 
of a full-grown salmon, how does its production of milt 
consist with the alleged general law P The answer must be 
in a great measure hypotheticaL If the salmon is (as it 
appears in its young state) a species of fresh-water trout, 
that has contracted the habit of annually migrating to the 
sea, where it finds a food on which it thrives — if the original 
size of this species was not much greater than that of the 
parr (which is nearly as large as some varieties of lake- trout 
and river-trout) — and if the limit of growth in the trout 
tribe is very indefinite, as we know it to be; then we 
may reasonably infer, that the parr has nearly the adult 
form and size of this species of trout, before it acquired 
its migratory habit ; and that this production of milt, is, 

* I owe to Mr Lubbock an important confirmation of this view. After stat- 
ing his belief, that between Crustaceans and Insects, there exists a physiological 
relation analogous to that which exists between water-vertebrata and Lind-yerte- 
brata ; he pointed out to me, that while among Insects, there is a definite limit 
of growth, and an accompanying definite commencement of reproduction, among 
Crustaceans, where growth has no definite limit, there is no definite, relation 
between the commencement of reproduction and the decrease or arrest of growth. 


in such case, a concomitant of the incipient decline of 
growth naturally arising in the species, when living under 
the conditions of its remote ancestors. If this be admitted, 
the immense subsequent growth of the parr into the salmon, 
must be regarded as due to a suddenly-increased facility in 
obtaining food — a facility which removes to a great distance 
the limit at which assimilation is balanced by expenditure ; 
and which has the effect, analogous to that produced in 
plants, of arresting the incipient reproductive process, and 
causing a resumption of growth. A confirmation of this 
view may be drawn from the fact, that when the parr, after 
its first migration to the sea, returns to fresh water, having 
increased in a few months from a couple of ounces to five or 
six pounds, it no longer shows any fitness for propagation : 
the grilse, or immature salmon, does not produce milt or 
spawn. But without citing further illustrations, or 

attempting to meet further difiiculties, it has, I think, been 
made sufficiently clear, that some such connexion as that al- 
leged, exists. Traversed, as is this relation between commence- 
ment of sexual reproduction and declining rate of growth, by 
various other relations, it is quite as manifest as we can 
expect it to be. 

The general law to which both homogenesis and hetero- 
genesis conform, thus appears to be, that the products of a 
fertilized germ go on accumulating by simple growth, so long 
as the forces whence growth results are greatly in excess of 
the antagonist forces ; but that when diminution of the one 
set of forces, or increase of the other, causes a considerable 
decline in this excess, and an approach towards equilibrium, 
fertilized germs are again produced. Whether the germ- 
product be organized round one axis, or round the many 
axes that arise by agamogenesis — whether the development 
be continuous or discontinuous ; matters not. Whether, as 
in concrete organisms like the higher animals, this approach 
to equilibrium results from that disproportionate increase of 
expenditure entailed by increase of size ; or whether, as in 


partially and wholly discrete organisms^ like most plants and 
many inferior animals, this approach to equilibrium results 
from absolute or relative decline of nutrition ; matters not. 
In any case, the recurrence of gamogenesis is associated with 
a more or less marked decrease in the excess of tissue-pro- 
ducing power. We cannot say, indeed, that a de- 
crease in this excess always results in gamogenesis ; for we 
have evidence to the contrary, in the fact that some organ- 
isms multiply for an indefinite period by agamogenesis only. 
Thus, the weeping willow, which has been propagated through- 
out Europe, does not seed in Europe ; and yet, as the weep- 
ing willow, by its large size and the multiplication of 
generation upon generation of lateral axes, presents the same 
causes of local innutrition as other trees, we cannot ascribe 
the absence of sexual axes to the continued predominance of 
nutrition. Among animals, too, the anomalous case of the 
Tineidce, a group of moths in which parthenogenetic mul- 
tiplication goes on for generation after generation, shows us 
that gamogenesis does not necessarily result from an approxi- 
mate balance of assimilation by expenditure. What we must 
say, is, that an approach towards equilibrium between the 
forces which cause growth and the forces which oppose 
growth, is the chief condition to the recurrence of gamo- 
genesis ; but that there are other imknown conditions, in the 
absence of which this approach to equilibrium is not followed 
by gamogenesis. 

§ 79. The above induction is an approximate answer to 
the question — JFhen does gamogenesis recur P but not to the 
question which was propounded — Why does gamogenesis re- 
cur P — WTit/ cannot multiplication be carried on in all cases, 
as it is in many cases^ by agamogenesis P As already said, 
biologic science is not yet advanced enough to reply. Mean- 
while, the evidence above brought together, suggests a cer- 
tain hypothetical answer, which it may be well to set down. 

Seeing as we do, on the one hand, that gamogenesis recurs 


only in individuals that are approaching towards a state of 
organic equilibrium ; and seeing, on the other hand, as we 
do, that the sperm-ceUs and germ-cells thrown off by such 
individuals, are cells in which developmental changes have 
ended in quiescence, but in which, after their imion, there 
arises a process of active cell-formation ; we may suspect 
that the approach towards a state of general equilibrium in 
such gamogenetic individuals, is accompanied by an approach 
towards molecular equilibrium in them ; and that the need 
for this union of sperm-cell and germ-cell, is the need for 
overthrowing this equilibrium, and re-establishing active mole- 
cular change in the detached germ — a, result which is pro- 
, bably effected by mixing the slightly different physiological 
imits of slightly different individuals. The several argu- 
ments that may be brought in support of this view, cannot 
be satisfactorily set forth until after the topics of Heredity 
and Variation have been dealt with. Leaving it for the pre- 
sent, I propose hereafter to reconsider this question, in con- 
nexion with sundry others that are raised by the phenomena 
of Genesis. 

Before ending the chapter, however, it may be well to note 
the relations between these different modes of multiplication, 
and the conditions of existence under which they are respect- 
ively habitual. While the explanation of the teleologist is 
untrue, it is often an obverse to the truth ; for though, on the 
hypothesis of Evolution, it is clear that things are not 
arranged thus or thus for the securing of special ends, it is 
also clear, that arrangements which do secure these special 
ends, tend coi^inually to establish themselves— are establish- 
ed by their fulfilment of these ends. Besides insuring a 
structural fitness between each kind of organism and its cir- 
cumstances, the working of ** natural selection " also insures 
a fitness between the mode and rate of multiplication of each 
kind of organism and its circumstances. We may, therefore, 
without any teleological implication, consider the fitness of 

GEN&SIS. 235 

homogenesiB and heterogenesis to the needs of the different 
classes of organisms which exhibit them. 

One of the facts to be observed, is, that heterogenesis pre- 
vails among organisms, of which the food, though abundant 
compared with their expenditure^ is dispersed in such a way 
that it cannot be appropriated in a wholesale manner. Pro- 
tophytay subsisting on diffused gases and decaying organic 
matter in a state of minute subdivisidn ; and Protozoa, to 
which food comes in the shape of extremely small floating 
particles ; are enabled by their rapid agamogenetio multipli- 
cation, to obtain materials for growth, better than they would 
do did they not thus continually divide and disperse in pur- 
suit of it. The higher plants, having for nutriment the car- 
bonic acid of the air and certain mineral components of the 
soil, show us modes of multiplication adapted to the fullest 
utilization of these substances. A herb, with but little power 
of forming the woody-fibre requisite to make a stem that can 
support wide-spreading branches, after producing a few sex- 
less axes, produces sexual ones ; and maintains its race better 
by the consequent early dispersion of seeds, than by a further 
production of sexless axes. But a tree, able to lift its suc- 
cessive generations of sexless axes high into the air, where 
each axis gets carbonic acid and light almost as freely as if it 
grew by itself, may with advantage go on budding-out sex- 
less axes year after year; since it thereby increases its sub- 
sequent power of budding-out sexual axes. Meanwhile, it 
may advantageously transform into seed-bearers, those axes 
which, in consequence of their less direct access to materials 
absorbed by the roots, are failing in their nutrition ; for in 
doing this, it is throwing-off from a point at which sus- 
tenance is deficient, a migrating groiq> of germs that may 
find sustenance elsewhere. The heterogenesis displayed by 
animals of the Ooelenterate type, has evidently a like utility. 
A polype, feeding on minute annelids and crustaceans, which, 
flitting through the water, come in contact with its tentacles; 


and limited to that quantity of prey which chance brings 
within its grasp ; buds out young polypes which, either as a 
colony or as dispersed individuals, spread their tentacles 
through a larger sp£U^ of water than the parent alone can ; 
and by producing them, the parent better insures the continu- 
ance of its species, than it would do if it went on slowly grow- 
ing imtil its nutrition was nearly balanced by its waste, and 
then multiplied by gamogenesis. Similarly with the Aphis. 
Living on sap sucked through its proboscis from tender shoots 
and leaves, and able thus to take in but a very small quan- 
tity in a given time, this creature's race is more likely to 
be preserved by a rapid asexual propagation of small indi- 
viduals, which disperse themselves over a wide but nowhere 
rich area of nutrition, than it would be did the individual 
growth continue so as to produce large individuals multiply- 
ing sexually. While at the same time we see, that when 
autimmal cold and diminishing supply of sap, put a check to 
growth, the recurrence of gamogenesis, and production of 
fertilized ova that remain dormant through the winter, is 
more favourable to the preservation of the race, than woidd be 
a further continuance of agamogenesis. On the 

other hand, it is obvious that among the higher animals^ 
living on food which, though dispersed, is more or less 
aggregated into large masses, this alternation of gamic and 
agamic reproduction ceases to be useM. The development 
of the germ-product into a single organism of considerable 
bulk, is in many cases a condition without which these large 
masses of nutriment could not be appropriated ; and here the 
formation of many individuals instead of one, would be fatal. 
But we still see the beneficial results of the general law — the 
postponement of gamogenesis until the rate of growth begins 
to decline. For so long as the rate of growth continues 
rapid, it is a proof that the organism gets food with great 
facility — ^that expenditure is not such as seriously to check 
accumulation ; and that the size reached is as yet not disad- 
vantageous — or rather, indeed, that it is advantageous. But 


when the rate of growth is much decreased by the compara- 
tively rapid increase of expenditiLre — when the excess of 
assimilative power is diminishing in such a way as to indi- 
cate its approaching disappearEOice ; it becomes needful for 
the maintenance of the species, that this excess shall be 
turned to the production of new individuals ; since, did 
growth continue until this excess disappeared through the 
complete balancing of assimilation and expenditure, the pro- 
duction of new individuals would be either impossible or fatal 
to the parent. And it is clear that " natural selection " will 
continually tend to determine the period at which gamo- 
genesis commences, in such a way as most favours the main- 
tenance of the race. 

Here, too> may fitly be pointed out the fact, that, by 
"natural selection,'* there will in every case be produced, the 
most advantageous proportion of males and females. If the 
conditions of life are such as to render a greater or less in- 
equality of the sexes beneficial to the species, in respect 
either of the number of the offipring, or the character of the 
offspring ; then, those varieties of the species which, from any 
cause, approach more than other varieties towards this 
beneficial degree of inequality, will be apt to supplant other 
varieties. And conversely, where equality in the number of 
males and females is beneficial, the equilibriimi will be main- 
tained by the dying out of such varieties as produce offspring 
among which the sexes are not balanced. 



§ 80. Already, in the last two chapters, the law of heredi- 
tary transmission has been tacitly assumed; as, indeed, it 
unavoidably is in all such discussions. Understood in its 
entirety, the law is, that each plant or animal produces 
others of like kind with itself : the likeness of kind consist- 
ing, not so much in the repetition of individual traits, as in 
the assumption of the same general structure. This truth has 
been rendered so familiar by daily illustration, as almost to 
have lost its significance. That wheat produces wheat — that 
existing oxen have descended from ancestral oxen — that every 
unfolding organism eventually takes the form of the class, 
order, genus, and species from which it sprang ; is a fact 
which, by force of repetition, has acquired in our minds 
almost the aspect of a necessity. It is in this, however, 
that Heredity is principally displayed : the phenomena com- 
monly referred to it, being quite subordinate manifestations. 
And, as thus understood. Heredity is universal. The various 
instances of heterogenesis lately contemplated, seem, indeed, 
to be at variance with this assertion. But they are not 
really so. Though the recurrence of like forms, is, in these in- 
stances, not direct but cyclical, still, the like forms do recur ; 
and when taken together, the group of forms produced during 
one of the cycles, is as much like the groups produced in pre- 
ceding cycles, as the single individual arising by homo- 
genesis, is like ancestral individuals. 


Wliile, however, the general truth that organisms of a 
given type uniformly descend from organisms of the same 
type, is so well established by infinite illustrations, as to have 
assumed the character of an axiom ; it is not universally 
admitted that non-typical peculiarities are inherited. While 
the botanist would be so incredulous if told that a plant of 
one class had produced a plant of another class, or that from 
seeds belonging to one order individuals belonging to another 
order had grown, that he would deem it needless to examine 
the evidence ; and while the zoologist would treat with con- 
tempt the assertion, that from the egg of a fish a reptile had 
arisen, or that an implacental mammal had borne a pla- 
cental mammal, or that an unguiculate quadruped had sprung 
from an ungulate quadruped, or even that from individuals 
of one species offspring of an allied species had proceeded ; 
yet there are botanists and zoologists who do not consider it 
certain, that the minor specialities of organization are trans- 
mitted from one generation to another. Some naturalists 
seem to entertain a vague belief, that the law of Heredity 
applies only to main characters of structure, and not to de- 
tails ; or, at any rate, that though it applies to such details 
as constitute differences of species, it does not apply to 
smaller details. The circumstance that the tendency to re- 
petition, is in a slight degree qualified by the tendency to 
variation (which, as we shall hereafter see, is but an indirect 
result of the tendency to repetition), leads some to doubt 
whether Heredity is unlimited. A careful weighing of the 
evidence, however, and a due allowance for the influences by 
which the minuter manifestations of Heredity are obscured, 
will remove the grounds for this scepticism. 

First in order of importance, comes the fact, that not only 
are there uniformly transmitted from an organism to its 
offspring, those traits of structure which distinguish the class, 
order, genus, and species ; but also those which distinguish 
the variety. We have numerous cases, among both plants 
and animals, where, by natural or artificial conditions, there 


have been produced divergent modifications of the same 
species ; and abundant proof exists that the members of any 
one sub-species, habitually transmit their distinctive pecu- 
liarities to their descendants. Agriculturists and 
gardeners can furnish unquestionable illustrations. Several 
varieties of wheat are known ; of which each reproduces 
itself. Since its introduction into England, there have been 
formed from the potato, a number of sub-species: some of them 
difiering greatly in their forms, sizes, qualities, and periods 
of ripening. Of peas, also, the like may be said. And the 
case of the cabbage-tribe, is often cited as showing the per- 
manent establishment of races that have diverged widely 
from a common stock. Among fruits and flowers, the multi- 
plication of kinds, and the continuance of each kind with 
certainty by agamogenesis, and to some extent by gamo- 
genesis, might be exemplified without end. • From all 
sides evidence may be gathered showing a like persistence of 
varieties in each species of animal. We have our distinct 
breeds of sheep, our distinct breeds of cattle, our distinct 
breeds of horses : each breed maintaining its characteristics. 
The several sorts of dogs, which, if we accept the physiolo- 
gical test, we must consider as all of one species, show us in 
a marked manner the hereditary transmission of small diflfer- 
ences — each sort, when kept pure, reproducing itself not 
only in size, form, colour, and quality of hair, but also in 
disposition and speciality of intelligence. Rabbits, too, have 
their permanently-established races. And in the Isle of Man, 
we have a tail-less kind of cat. Even in the absence 
of other evidence, that which ethnology furnishes would 
suffice. Grant them to be derived from one stock, and the 
varieties of man yield proof upon proof that non-specific 
traits of structure are bequeathed from generation to gener- 
ation. Or grant only that there is evidence of their deriva- 
tion from several stocks, and we still have, between races de- 
scended from a common stock, distinctions which prove the 
inheritance of minor peculiarities. Besides seeing that 


negroes continue to produce negroes, copper-coloured men to 
produce men of a copper colour, and the fair-skinned races 
to perpetuate their fair skins — ^besides seeing that the broad- 
faced and flat-nosed Galmuck begets children with broad faces 
and flat noses, while the Jew bequeaths to his offspring the 
features which have so long characterized Jews ; we see that 
those small unlikenesses which distinguish more nearly-allied 
varieties of men, are maintained from generation to generation. 
In Germany, the ordinary shape of skull is appreciably differ- 
ent from that common in Britain: near akin though the 
Qermans are to the British, The average Italian face con- 
tinues to be unlike the faces of northern nations. The French 
character is now, as it was centuries ago, contrasted in sundry 
respects with the characters of neighbouring peoples. Nay, 
even between races so closely allied as the Scotch Celts, the 
Welch Celts, and the Irish Celts, appreciable differences of 
form and nature have become established. 

That sub-species and sub-sub-species, thus exemplify that 
same general law of inheritance which shows itself in the per- 
petuation of ordinal, generic, and specific peculiarities ; is 
strong reason for the belief that this general law is unlimited 
in its application. In addition to the warrant which this be- 
lief derives from evidence of this kind, it has also the support 
of still more special evidence. Numerous illustrations of He- 
redity are yielded by experiment, and by direct observation of 
successive generations. They are divisible into two classes. 
In the one class come cases where congenital peculiarities, 
not traceable to any obvious causes, are bequeathed to de- 
scendants. In the other class come cases where the peculiar- 
ities thus bequeathed are not congenital, but have resulted 
from changes of functions during the lives of the individuals 
bequeathing them. We will consider first the cases that 
come in the first class. 

§ 81. Note at the outset the character of the chief testi- 
mony. Excluding those inductions that have been so fully 



verified as to rank with exact science^ there are no inductions 
so trustworthy as those which have undergone the mercantile 
test. When we have thousands of men whose profit or loss 
depends on the truth of the inferences they draw from simple 
and perpetually-repeated observations; and when we find 
that the inference arrived at, and handed down from genera- 
tion to generation of these deeply-interested observers, has 
become an unshakable conviction ;- we may accept it without 
hesitation. In breeders of animals we have such a class, led 
by such experiences, and entertaining such a conviction — the 
conviction that minor peculiarities of organization are in- 
herited as well as major peculiarities. Hence the immense 
prices given for successM racers, bulls of superior forms, 
sheep that have certain desired peculiarities. Hence the 
careM record of pedigrees of high-bred horses and sporting 
dogs. Hence the care taken to avoid intermixture with in- 
ferior stocks. Citing the highest authorities respecting the 
effects of breeding from animals having certain superiorities, 
with the view of propagating those superiorities, Mr Darwin 
writes : — " Youatt, who was probably better acquainted with 
the works of agriculturists than almost any other individual, 
and who was himself a very good judge of an animal, speaks 
of the principle of selection as * that which enables the agri- 
culturist not only to modify the character of his flock, but to 
change it altogether. It is the magician's wand, by means of 
which he may summon into life whatever form and mould he 
pleases.' '' Lord Somerville, speaking of what breeders have 
done for sheep, says : — " It would seem that they had chalked 
upon a wall a form perfect in itself and then given it exist- 
ence.'* That most skilful breeder. Sir John Sebright, used to 
gay, with respect to pigeons, that "he would produce any 
given feather in three years, but it would take him six years 
to obtain head and beak." In all which statements the 
tacit assertion is, that individual traits are bequeathed 
from generation to generation ; and that when they are 
not brought into conflict with opposite traits, they may be 


SO perpetuated and increased as to beoome permanent dis- 

Of special instances, there are many besides that of the oft- 
en-cited Otter-breed of sheep, descended from a single short- 
legged lamb, and that of the six-fingered Gratio KeUeia, who 
transmitted his peculiarity in diflferent degrees, to several of 
his children and to some of his grandchildren. In a paper con- 
tributed to the Edinburgh New Philosophical Journal for July 
1863, Dr Struthers gives several cases of hereditary digital 
variations. Esther P — , who had six fingers on one hand, be- 
queathed this malformation, along some lines of her descend- 
ants, for two, three, and four generations. A — S — inherited 
an extra digit on each hand and each foot from his father ; 
and C — G — , who also had six fingers and six toes, had an aunt 
and a grandmother similarly formed. A collection of evidence 
has been made by Mr Sedgwick, and published by him in the 
Medico- Chirurgical Remew for April and for July 1863, in 
two articles on " The Influence of Sex in limiting Hereditary 
Transmission." From these articles are selected the following 
cases and authorities : — Augustin Duforet, a pastry-cook of 
Douai, who had but two instead of three phalanges to all his 
fingers and toes, inherited this malformation from his grand- 
father and father, and had it in common with an imcle and 
nimierous cousins. An account has been given by Dr Lepine, 
of a man with only three fingers on each hand and four toes 
on each foot, and whose grandfather and son exhibited the 
like anomaly. B^chet describes Victoire Barr^ as a woman 
who, like her father and sister, had but one developed finger 
on each hand, and but two toes on each foot, and whose mon- 
strosity re-appeared in two daughters. And there is a case 
where the absence of two distal phalanges on the hands was 
traced for two generations. The various recorded instances 
in which there has been transmission from one generation to 
another, of webbed-fingers, of webbed-toes, of hare-lip, of 
congenital luxation of the thigh, of absent patellsB, of 
club-foot, &c., would occupy more space than can here be 



spared. Defects in the organs of sense are also not 

unfrequently inherited. Four sisters, their mother, and 
grandmother, are described by Duval as similarly affected by 
cataract. Prosper Lucas details an example of hereditary am- 
aurosis affecting the females of a family for three generations. 
Duval, Graffe, Dufon, and others testify to like cases coming 
under their observation.* Deafness, too, is occasionally trans- 
mitted from parent to child. There are deaf-mutes whose 
imperfections have been derived from ancestors; and mal« 
formations of the external ears have also been perpetuated in 
offspring. Of transmitted peculiarities of the skin 

and its appendages, many illustrations have been noted. One 
is that of a family remarkable for enormous black eyebrows ; 
another that of a family in which every member had a lock of 
hair of a lighter colour than the rest on the top of the head ; 
and there are also instances of congenital baldness being 
hereditary. Entire absence of teeth, absence of particular 
teeth, and anomalous arrangements of teeth, are recorded as 
traits that have descended to children. And we have evidence 
that soundness and unsoundness of teeth are transmissible. 

The inheritance of such diseases as gout, consumption, and 
insanity, is universally admitted. Among the less-common 
diseases of which the descent from one generation to another 
has been observed, are, ichthyosis, leprosy, pityriasis, sebace- 
ous tumours, plica polonica, dipsomania, somnambulism, cata- 
lepsy, epilepsy, asthma, apoplexy, elephantiasis. General 
nervousness displayed by parents, almost always re-^appears 
in their children. Even a bias towards suicide appears to 
be sometimes hereditary, 

§ 82. To prove the transmission of those structural pecu- 
liarities that have resulted from functional peculiarities, is, 

• While this chapter is passing through the press, I learn from Mr White 
Cooper, that not only are near sight, long sight, dull sight, and squinting, here- 
ditary ; hut that a peculiarity of vision confined to one eye, is frequently trans- 
mitted—re-appearing in the same eye in offspring. 


for several reasons, comparatively difficult. Changes pro- 
duced in the sizes of parts by changes in their amounts of 
action, are mostly unobtrusive. A muscle that has increased 
in bulk, is so obscured by natural or artificial clothing, that un- 
less the alteration is extreme it passes without remark. Such 
nervous developments as are possible in the course of a single 
life, cannot be seen externally. Visceral modifications of a 
normal kind, are observable but obscurely, or not at all. And 
if the changes of structure worked in individuals by changes 
in their habits, are thus difficult to trace ; still more difficult 
to trace must be the transmission of them — ^further hidden, 
as this is, by the influence of other individuals that are often 
otherwise modified by other habits. Moreover, such special- 
ities of structure as are due to specialities of function, are 
usually entangled with specialities of structure that are, or 
may be, due to selection, natural or artificial. In the majority 
of cases, it is impossible to say that a structural peculiarity 
which seems to have arisen in. ofispring from a functional 
peculiarity in the parent, is wholly independent of some 
congenital peculiarity of structure in the parent, which in- 
duced this functional peculiarity. We are restricted to 
cases with which natural or artificial selection can have had 
nothing to do ; and such cases are difficult to find. Some, 
however, may here be noted. 

A species of plant that has been transferred from one soil 
or climate to another, frequently undergoes what botanists 
call " a change of habit " — a change which, without aflfecting 
its specific characters, is yet conspicuous. In its new locality, 
the species is distinguished by leaves that are much larger, 
or much smaller, or difierently shaped, or more fleshy ; or 
instead of being, as before, comparatively smooth, it becomes 
hairy; or its stem becomes woody instead of being herbaceous; 
or its branches, no longer growing upwards, assume a droop- 
ing character. Now these " changes of habit" are clearly de- 
termined by functional changes. Occurring, as they do, in 
many individuals that have undergone the same transportation, 


they cannot be classed as '^ spontaneous variations." They 
are modifications of structure, consequent on modifications of 
function, that have been produced by modifications in the 
actions of external forces. And as these modifications re-ap- 
pear in succeeding generations, we have, in them, examples 
of functionally-estabEshed variations that are hereditarily 
transmitted. Further evidence is supplied by what 

are called ^' sports " in plants. These are of two kinds — ^the 
gamogenetic and the agamogenetic. The gamogenetic may 
be ascribed wholly to " spontaneous variations ;** or if they are 
partly due to the inheritance of structural changes that are 
produced by fimctional changes^ this cannot be proved. But 
where the individuals displaying the variations arise by 
agamogenesis, the reverse is the case: spontaneous variation 
is out of the question ; and the only possible interpretation is 
deviation of structure caused by deviation of function. A 
new axis which buds out from a parent-axis, assumes an un- 
like character — gives off lobed leaves in place of single leaves, 
or has an otherwise different mode of growth. This change 
of structure implies change in the developmental actions 
which produced the new bud — change, that is, in the actions 
going on in the parent shoot — functional change. And 
since the modified structure thus impressed on the new shoot 
by modified function, is transmitted by it to all the shoots 
it bears ; we are obliged to regard the case as one of acquired 
modification that has become hereditary. 

Evidence of analogous changes in animals, is difficult to 
disentangle. Only among domesticated animals, have we any 
opportunity of tracing the effects of altered habits ; and here, 
in nearly all cases, artificial selection has obscured the results. 
Still, there are some facts which seem to the point. Mr 
Darwin, while ascribing almost wholly to ^^ natural selection '' 
the production of those modifications which eventuate in 
differences of species, nevertheless admits the effects of use and 
disuse. He says — '^ I find in the domestic duck that the bones 
of the wing weigh less and the bones of the leg more, in pro- 


portion to the whole skeleton, than do the same bones in the 
wild duck ; and I presume that this change may be safely 
attributed to the domestic duck flying much less, and walking 
more, than its wild parent. The great and inherited develop- 
ment of the udders in cows and goats in countries where they 
are habitually milked, in comparison with the state of these 
organs in other countries, is another instance of the effect of 
use. Not a single domestic animal can be named which has 
not in some country drooping ears ; and the view suggested by 
some authors, that the drooping is due to the disuse of the 
muscles of the ear, from the animals not being much alarmed 
by danger, seems probable." Again — " The eyes of moles and 
of some burrowing rodents are rudimentary in size, and in 
some cases are quite covered up by skin and fur. This state 
of the eyes is probably due to gradual reduction from disuse, 
but aided perhaps by natural selection." * * * " It is well 
known that several animals, belonging to the most differ- 
ent classes, which inhabit the caves of Styria and of Kentucky, 
are blind. In some of the crabs the footstalk of the eye re- 
mains, though the eye is gone ; the stand for the telescope is 
there, though the telescope with its glasses has been lost. As 
it is difficult to imagine that eyes, though useless, could be in 
any way injurious to animals living in darkness, I attribute 
their loss wholly to disuse." The direct inheritance of an ac-. 
quired peculiarity is sometimes observable. Mr Lewes gives 
a case. He ^' had a puppy taken from its mother at six weeks 
old, who, although never taught, ' to beg' (an accomplishment 
his mother had been taught), spontaneously took to begging 
for everything he wanted when about seven or eight months 
old : he would beg for food, beg to be let out of the room, 
and one day was found opposite a rabbit hutch begging for 
rabbits." Instances are on record, too, of sporting dogs which 
spontaneously adopted in the field, certain modes of behaviour 
which their parents had learnt. 

But the best examples of inherited modifications produced 
by modifications of function, occur in the human race. To no 


other cause can be ascribed the rapid metamorphoBes under- 
gone by the Britiflh races when placed in new conditions. It 
is notorious that« in the United States^ the descendants of the 
immigrant Irish lose their Celtic aspect^ and become Ameri- 
canized. This cannot be ascribed to intermarriage with 
Americans; since the feeling with which Irish are regard- 
ed by Americans, prevents any considerable amount of inter- 
marriage. Equally marked is the case of the immigrant 
Oermans, who, though they keep themselves very much 
apart, rapidly assume the prevailing type. To say that 
" spontaneous variation " increased by natural selection, can 
have produced this effect, is going too far. Races so numer- 
ous, cannot have been supplanted in the course of two or 
three generations by varieties springing from them. Hence 
there is no escape from the conclusion, that physical and so- 
cial conditions have here wrought modifications of function 
and structure, which offspring have inherited and increased. 
Similarly with special cases. In the Cychpcedia of Practical 
Medictne, VoL II. p. 419, Dr Brown states that he " has in 
many instances observed in the case of individuals whose 
complexion and general appearance has been modified by re- 
sidence in hot climates, that children bom to them subse- 
quently to such residence, have resembled them rather in 
their acquired than primary mien." 

- Some special modifications of organs caused by special 
changes in their Amotions, may also be noted. That large 
hands are inherited by men and women whose ancestors 
led laborious lives ; and that men and women whose descent, 
for many generations, has been from those unused to manual 
labour, commonly have small hands ; are established opinions. 
It seems very unlikely that in the absence of any such con- 
nexion, the size of the hand should thus have come to be 
generally regarded as some index of extraction. That there 
exists a like relation between habitual use of the feet and large- 
ness of the feet, we have strong evidence in the customs of the 
Chinese. The torturing practice of artificially arresting the 


growth of the feet, could never have become established among 
the ladies of China, had they not found abundant proof 
that a small foot was significant of superior rank — ^that is 
of a luxurious life — that is of a life without bodily 
labour. There is some evidence, too, that modifica- 

tions of the eyes, caused by particular uses of the eyes, are 
inherited. Short sight appears to be uncommon in rural 
populations ; but it is frequent among classes of people who 
use their eyes much for reading and writing ; and in these 
classes, short sight is often congenital. Still more marked is 
this relation in Qermany. There, the educated classes are no- 
toriously studious ; and judging from the numbers of young 
Germans who wear spectacles, there is reason to think that 
congenital myopia is very frequent among them. 

Some of the best illustrations of functional heredity, are 
furnished by the mental characteristics of human races. Cer- 
tain powers which mankind have gained in the course of civil- 
ization, cannot, I think, be accounted for, without admitting 
the inheritance of acquired modifications. The musical faculty 
is one of these. To say that " natural selection" has developed 
it, by preserving the most musically endowed, seems an in- 
adequate explanation. Even now that the development and 
prevalence of the faculty have made music an occupation by 
which the most musical can get sustenance and bring up 
families ; it is very questionable whether, taking the musical 
life as a whole, it has any advantage over others in the 
struggle for existence and multiplication. Still more if we 
look back to those early stages through which the faculty must 
have passed, before definite perception of melody was arrived 
at, we fail to see how those possessing the rudimental facidty 
in a somewhat greater degree than the rest, would thereby be 
enabled the better to maintain themselves and their children. 
If so, there is no explanation but that the habitual association 
of certain cadences of human speech with certain emotions, 
has slowly established in the race an organized and inherited 
connexion between such cadences and such emotions ; that the 


combination of such cadences^ more or less idealized^ which 
constitutes melody^ has all along had a meaning in the average 
mind, only because of the meaning which cadences had acquired 
in the ayerage mind ; and that by the continual hearing and 
practice of melody, there has been gained and transmitted an 
increasing musical sensibility. Confirmation of this 

yiew may be drawn from individual cases. Grant that among 
a people endowed with musical facility to a certain degree, 
spontaneous variation will occasionally produce men possessing 
it in a higher degree ; it cannot be granted that spontaneous 
variation accounts for the frequent production, by such highly- 
endowed men, of men still more highly endowed. On the 
average, the offspring of marriage with others not similarly 
endowed, will be less distinguished rather than more distin* 
guished. The most that can be expected is, that this unusual 
amount of faculty shall re-appear in the next generation undi- 
minished. How then shall we explain cases like those of Bach, 
Mozart, and Beethoven, who were aU sons of men having un- 
usual musical powers, but who greatly excelled their fathers 
in their musical powers P What shall we say to the facts, 
that Haydn was the son of the organist, that Hummel was 
bom to a music master, and that Weber's father was a dis- 
tinguished violinist? The occurrence of so many cases in 
one nation, within a short period of time, cannot rationally 
be ascribed to the coincidence of *' spontaneous variations." It 
can be ascribed to nothing but inherited developments of 
structure, caused by augmentations of function. 

But the clearest proof that structural alterations caused by 
alterations of function, are inherited, occurs when the alter- 
ations are morbid. '* Certain modes of living engender gout ; '* 
and gout is transmissible. It is well known that in persons pre- 
viously healthy, consumption may be produced by un& vourable 
conditions of life — ^by bad and insufficient food ; by foul, damp, 
unventilated habitations ; and even by long-continued anxiety. 
It is still more notorious that the consumptive diathesis is 
conveyed from parent to child. Unless, then, a distinction 


be assumed between constitutional consumption and con- 
sumption induced by unwholesome conditions — unless it be 
asserted that consumption of unknown origin is transmiss- 
ible^ while functionally-produced consumption is not ; it 
must be admitted that those changes of structure from which 
the consumptive diathesis results, may be caused in parents 
by changes of function, and may be inherited by their chil- 
dren. Most striking of all, however, is the fact lately 
brought to light, that functional disorders artificially estab- 
Ushed, may be conveyed to offspring. Some few years since 
M. Brown-Sequard, in the course of inquiries into the nature 
and causes of epilepsy, hit on a method by which epilepsy 
could be originated. Guinea-pigs were the creatures on 
which, chiefly, he experimented ; and eventually, he disco- 
vered the remarkable fact, that the young of these epileptic 
guinea-pigs were epileptic : the fimctionally-established 
epilepsy in the parents, became constitutional epilepsy in the 
offspring. Here we have an instance which, standing even 
alone, decides the question. We have a special form of nervous 
action, not caused by any natural variation of structure that 
had arisen spontaneously in the organism, but one caused 
by a certain incidence of external forces. We have this 
special form of nervous action becoming confirmed by re- 
petition : the fits are more and more easily induced — there is 
established the epileptic habit. That is to say, the connected 
nervous actions constituting a fit, produce in the nervous 
system such changes of structure, that subsequent connected 
nervous actions of like kind, follow one another with increased 
readiness. And that this epileptic habit is inherited, proves 
conclusively that these structural modifications worked by 
functional modifications, are impressed on the whole organism 
in such way as to affect the reproductive centres, and cause 
them to unfold into organisms that exhibit like modifications. 
Evidence nearly allied to this, and scarcely less significant, 
is famished by that transmission of general nervousness, no- 
ticed in the last section. Nervousness is especially common 


among classes of people wlio tax their brains much. Among 
these classes, we daily see this constitutional modification 
produced by excess of function, in men whose progenitors 
were not nervous ; and the children of such men habitually 
inherit more or less of the modification. 

§ 83. Two modified manifestations of Heredity remain to be 
noticed. The one is the re-appearance in offipring, of traits 
not borne by the parents, but borne by the grandparents or by 
remoter ancestors. The other is the limitation of Heredity by 
sex — ^the restriction of certain transmitted peculiarities to 
o&pring of the same sex as the parent possessing these 

Atavism, which is the name given to the recurrence of 
ancestral traits, is proved by many and varied facts. In the 
picture-galleries of old families, and on the monumental 
brasses in the adjacent churches, are often seen types of 
feature that are still, from time to time, repeated in members of 
these families. It is matter of common remark that some con- 
stitutional diseases, such as gout and insanity, after missing a 
generation, will show themselves in the next. Dr Struthers, 
in his above-quoted paper on ^' Variation in the Number of 
Fingers and Toes, and of the Phalanges, in Man," gives cases 
of malformations that were common to grandparent and 
grandchild, but of which the parent had no trace. M. Girou 
(as quoted by Mr Sedgwick) says — " One is often surprised 
to see lambs black, or spotted with black, bom of ewes and 
rams with white wool, but if one takes the trouble to go 
back to the origin of this phenomenon, it is found in the an- 
cestors." Instances still more remarkable, in which the re- 
moteness of the ancestors copied is very great, are given by 
Mr Darwin. He points out that in crosses between varieties 
of the pigeon, there will sometimes re-appear the plumage of 
the original rock-pigeon, from which these varieties descend- 
ed ; and he instances the faint zebra-like markings occasion- 
ally traceable in horses, as having probably a like meaning. 


The limitation of Heredity by sex, cannot yet be regarded 
as established. While in many cases it seems clearly mani* 
fested ; it is in other oases manifested to a very small degree, 
if at all. In Mr Sedgwick's essays, already named, will be 
found evidenoe implying that there exists some saoh tendency 
to limitation, which does or does not show itself distinctly, 
according to the nature of the organic modification to be 
conveyed. But more facts must be collected before any 
positiye conclusion can be reached. 

§ 84. A positive explanation of Heredity is not to be expected 
inthepresent state of Biology. Wecan look for nothing beyond 
a simplification o1^ the problem ; and a reduction of it to the 
same category with certain other problems which also admit 
of hypothetical solution only. If an hypothesis which certain 
other wide-spread phenomena have already thrust upon us, 
can be shown to render the phenomena of Heredity more in- 
telligible than they at present seem, we shall have reason to 
entertain it. The applicability of any method of interpreta- 
tion to two difierent but allied classes of facts, is evidence of 
its truth. 

The power which organisms display of reproducing lost 
parts, we saw to be inexplicable except on the assumption 
that the imits of which any organism is built have an innate 
tendency to arrange themselves into the shape of that organ- 
ism (§ 65), We inferred that these units must be the pos- 
sessors of special polarities, resulting from their special struc- 
tures ; and that by the mutual play of their polarities they are 
compelled to take the form of the species to which they belong. 
And the instance of the Begonia phylhmaniaca left us no 
escape from the admission that the ability thus to arrange 
themselves, is latent in the units contained in every undiffer- 
entiated cell. Quite in harmony with this conclusion, 
are certain implications since noticed, respecting the characters 
of sperm-cells and germ-cells. We saw sundry reasons for 
rejecting the supposition that these are highly-specialized cells, 


and for aocepting the opposite supposition, that they are cells 
differing from others rather in being unspecialized. And here 
the assumption to which we seem driven by the ensemble of 
the evidence, is, that sperm-cells and germ-cells are essentially 
nothing more than vehicles, in which are contained small 
groups of the physiological units in a fit state for obeying their 
proclivity towards the structural arrangement of the species 
they belong to. 

Thus the phenomena of Heredity are seen to assimilate 
with other phenomena ; and the assumption which these 
other phenomena thrust on us, appears to be equally 
thrust on us by the phenomena of Heredity. We must con- 
clude that the likeness of any organism to either parent, is 
conveyed by the special tendencies of the physiological units 
derived from that parent. In the fertilized germ we have 
two groups of physiological units, slightly different in their 
structures. These slightly-different units, severally multiply 
at the expense of the nutriment supplied to the unfolding germ 
— each kind moulding this nutriment into units of its own 
type. Throughout the process of evolution, the two kinds of 
units, mainly agreeing in their polarities and in the form 
which they tend to build themselves into, but having minor 
differences, work in unison to produce an organism of the 
species from which they were derived, but work in antagonism 
to produce copies of their respective parent-organisms. And 
hence ultimately results, an organism in which traits of the 
one are mixed with traits of the other. 

If the likeness of ofepring to parents is thus determined, it 
becomes manifest, a priori, that besides the transmission of 
generic and specific peculiarities, there will be a transmis- 
sion of those individual peculiarities which, arising without 
assignable causes^ are classed as " spontaneous." For if the 
assumption of a special arrangement of parts by an organism, 
is due to the proclivity of its physiological units towards 
that arrangement ; then the assumption of an arrangement 
of parts slightly different from that of the species, implies 


physiological units slightly unlike those of the species ; and 
these slightly-unKke physiological units, communicated 
through the medium of sperm-cell or germ-cell, will tend, in 
the offspring, to build themselves into a structure similarly 
diverging from the average of the species. 

It is not equally manifest, d, priori, however, that on this hy- 
pothesis, alterations of structure caused by alterations of func- 
tion, must be transmitted to offspring. It is not obvious that 
change in the form of a part, caused by changed action, in- 
volves such change in the physiological units throughout the 
organism^ that these, when groups of them are thrown off in 
the shape of reproductive centres, will unfold into organisms 
that have this part similarly changed in form. Indeed, when 
treating of Adaptation (§ 69), we saw that an organ modified 
by increase or decrease of function, can but slowly so re-act 
on the system at large, as to bring about those correlative 
changes required to produce a new equilibrium ; and yet only 
when such new equilibrium has been established, can we ex- 
pect it to he fully expressed in the modified physiological units 
of which the organism is built — only then can we count 
on a complete transfer of the modification to descendants. 
Nevertheless, that changes of structure caused by changes 
of action, must also be transmitted, however obscurely, from 
one generation to another, appears to be a deduction from 
first principles — or if not a specific deduction, stiU, a general 
implication. For if an organism A, has, by any peculiar 
habit or condition of life, been modified into the form A, it 
follows inevitably, that all the functions of A', reproductive 
function included, must be in some degree different from the 
functions of A. An organism being a combination of 
rhythmicaUy-acting parts in moving equilibrium, it is im- 
possible to alter the action and structure of any one part, 
without causing alterations of action and structure in all the 
rest; just as no member of the Solar System could be modi- 
fied in motion or mass, without producing re-arrangements 
throughout the whole Solar System. And if the organism A, 


when changed to A', must be changed in all its functions ; 
then the offspring of A' cannot be the same as they would 
have been had it retained the form A. It involves a denial 
of the persistence of force to say that A may be changed 
into A, and may yet beget offipring exactly like those it 
would have begotten had it not been so changed. That the 
change in the offspring must, other things equal, be in the 
same direction as the change in the parent, we may dimly see 
is implied by the fact, that the change propagated throughout 
the parental system is a change towards a new state of 
equilibrium — a change tending to bring the actions of all 
organs, reproductive included, into harmony with these new 
actions. Or, bringing the question to its ultimate and 
simplest form, we may say that as, on the one hand, phy- 
siological units will, because of their special polarities, build 
themselves into an organism of a special structure ; so, on 
the other hand, if the structure of this organism is modified 
by modified function, it will impress some corresponding 
modification on the structures and polarities of its units. The 
units and the aggregate must act and re-act on each other. 
The forces exercised by each unit on the aggregate and by 
the aggregate on each unit, must ever tend towards a balance. 
If nothing prevents, the units will mould the aggregate into 
a form in equilibrium with their pre-existing polarities. If, 
contrariwise, the aggregate is made by incident actions to 
take a new form, its forces must tend to re-mould the units 
into harmony with this new form. And to say that the 
physiological units are in any degree so re* moulded as to bring 
their polar forces towards equilibrium with the forces of the 
modified aggregate, is to say that when separated in the 
shape of reproductive centres, these units will tend to build 
themselves up into an aggregate modified in the same di- 



§ 85. Equally conspicuous with the truth that every organ- 
ism bears a general likeness to its parents, is the truth that 
no organism is exactly like either parent. Though similar 
to both in generic and specific traits, and usually, too, in those 
traits which distinguish the variety, it diverges in numer- 
ous traits of minor importance. No two plants are indistin- 
guishable ; and no two animals are without differences. 
Yariation is co-extensive with Heredity. 

The degrees of variation have a wide range. There are 
deviations so small as to be not easily detected ; and there 
are deviations great enough to be called monstrosities. In 
plants, we may pass from cases of slight alteration in the 
shape or texture of a leaf, to cases where, instead of a flower 
with its calyx above the seed-vessel, there is produced a flower 
with its calyx below the seed-vessel ; and while in one 
animal, there arises a scarcely noticeable unlikeness in the 
length or colour of the hair, in another, an organ is absent, 
or a supernumerary organ appears. Though small variations 
are by far the most general, yet variations of considerable 
magnitude are not uncommon ; and even those variations 
constituted by additions or suppressions of parts, are not so 
rare as to be excluded from the list of causes by which 
organic forms are changed. Cattle without horns are fre- 
quent. Of sheep there are horned breeds and breeds that 



have lost their homB. At one tiiue^ there existed ia Scot- 
land a race of pigs with solid feet instead of cleft feet. In 
pigeons, according to Mr Darwin^ '' the number of the cau- 
dal and sacral vertebrae vary ; as does the number of the 
ribs, together with their relative breadth and the presence of 

That variations both small and large which arise without 
any specific assignable cause, tend to become hereditary, was 
shown in the last chapter. Indeed the evidence which proves 
Heredity in its smaller manifestations, is the same evidence 
which proves Variation ; since it is only when there occur vari- 
ations, that the inheritance of anything beyond the structural 
peculiarities of the species, can be proved. It remains here, 
however, to be observed, that the transmission of variations 
is itself variable ; and that it varies both in the direction of 
decrease and in the direction of increase. An individual trait 
of one parent, may be so counteracted by the influence of the 
other parent, that it may not appear in the of&pring ; or not 
being so counteracted, the ofl&pring may possess it, perhaps 
in an equal degree or perhaps in a less degree ; or the off- 
spring may exhibit the trait in even a still higher degree. 
Of the illustrations of this, one must suffice. I quote it from 
the essay by Dr Struthers, referred to in the last chapter. 

" The great-great-grandmother, Esther P (who mar- 
ried A L ), had a sixth little finger on one hand. Of 

their eighteen children (twelve daughters and six sons), only 
one (Charles) is known to have had digital variety. We 
have the history of the descendants of three of the sons, 
Andrew, Charles, and James. 

" (1.) Andrew L had two sons, Thomas and Andrew ; 

and Thomas had two sons all without digital variety. Here 
we have three successive generations without the variety 
possessed by the great-grandmother showing itself. 

"(2.) James L , who was normal, had two sons and 

seven daughters, also normal. One of the daughters became 
Mrs J (one of the informants), and had three daughters 


and five sons, all normal except one of the sons, James J , 

now 8Bt. 17, who had six fingers on each hand. * * * 

** In this branch of the descendants of Esther, we see it 
passing over two generations and reappearing in one member 
of the third generation, and now on both hands. 

" (3.) Charles L , the only child of Esther who had 

digital variety, had six fingers on each hand. He had three 
sons, James, Thomas, and John, all of whom were born with 
six fingers on each hand, while John has also a sixth toe on 
one foot. He had also five other sons and four daughters, 
all of whom were normal. 

" (a.) Of the normal children of this, the third generation, 
the five sons had twelve sons and twelve daughters, and the 
four daughters have had four sons and four daughters, being 
the fourth generation, all of whom were normal. A fifth 
generation in this sub-group consists as yet of only two boys 
and two girls, who are also normal. 

" In this sub-branch, we see the variety of the first gener- 
ation present in the second, passing over the third and 
fourth, and also the fifth as far as it has yet gone. 

" (6.) James had three sons and two daughters, who are 

" (c.) Thomas had four sons and five daughters, who are 
normal ; and has two grandsons, also normal. 

" In this sub-branch of the descent, we see the variety of 
the first generation, showing itself in the second and third, 
and passing over the fourth, and (as far as it yet exists) 
the fifth generation. 

" {d.) John L (one of the infonnants) had six fingers, 

the additional finger being attached on the outer side, as in 
the case of his brothers James and Thomas. All of them 
had the additional digits removed. John has also a sixth 
toe on one foot, situated on the outer side. The fifth and 
sixth toes have a common proximal phalanx, and a common 
integument invests the middle and distal phalanges, each 
having a separate nail. 

17 • 


*' John L " has a son who is normal, and a daughter, 

Jane, who was born with six fingers on each hand and six toes 
on eac^ foot. The sixth fingers were removed. The sixth 
toes are not wrapped with the fifth as in her father's case^ 
but are distinct from them. The son has a son and daughter, 
who, like himself, are normal. 

" In this, the most interesting sub-branch of the descent, 
we see digital increase, which appeared in the first generation 
on one limb, appearing in the second on two limbs, the 
hands ; in the third on three limbs, the hands and one foot ; 
in the fourth on all the four limbs. There is as yet no fifth 
generation in uninterrupted transmission of the variety. 
The variety does not yet occur in any number of the fifth 
generation of Esther's descendants, which consists, as yet, 
only of three boys and one girl, whose parents were normal, 
and of two boys and two girls, whose grandparents were 
normal. It is not known whether in the case of the great- 
great-grandmother, Esther P , the variety was original 

or inherited."* 

§ 86. Where there is great uniformity among the mem- 
bers of a species, the divergences of offspring from the 
average type, are usually small; but where, among the 
members of a species, considerable unlikenesses have once 
been established, unlikenesses among the offspring are fre- 
quent and great. Wild plants growing in their natural 
habitats, are uniform over large areas, and maintain from 
generation to generation like structures; but when cul- 
tivation has caused appreciable differences among the mem- 
bers of any species of plant, extensive and nimierous deviations 
are apt to arise. Similarly, between wild and domesticated 

* This remarkable case appears to militate against the conclusion, drawn some 
few pages back, that the increase of a peculiarity by coincidence of ** spontaneous 
variations " in successive generations, is very improbable ; and that the special 
superiorities of musical composers cannot have thus arisen. The reply is, that the 
extreme frequency of the occurrence among so narrow a class as that of musical 
composers, forbids the interpretation thus suggested. 


animals of the same species, we see the contrast, that though 
the homogeneous wild race maintains its type with great per- 
sistence, the comparatively heterogeneous domestic race fre- 
quently produces individuals more unlike the average type 
than the parents are. 

Though unlikeness among progenitors is one antecedent 
of variation, it is by no means the sole antecedent. Were 
it so, the young ones successively born to the same parents 
would be alike. If any peculiarity in a new organism 
were a direct resultant of the structural differences between the 
two organisms which produced it ; then aU subsequent new 
organisms produced by these two, would show the same pecu- 
liarity. But we know that the successive offspring have differ- 
ent peculiarities : no two of them are ever exactly alike. 

One cause of such structural variation in progeny, is 
functional variation in parents. Proof of this is given by 
the fact that, among the progeny of the same parents, there is 
more difference between those begotten under different con- 
stitutional states, than between those begotten under the 
same constitutional state. It is notorious that twins are 
more nearly alike than children borne in succession. The 
functional conditions of the parents being the same for twins, 
but not the same for their brothers and sisters (all other ante- 
cedents being constant) ; we have no choice but to admit that 
variations in the functional conditions of the parents, are the 
antecedents of those greater unlikenesses which their brothers 
and sisters exhibit. 

Some other antecedent remains, however. The parents 
being the same, and their constitutional states the same, va- 
riation, more or less marked, still manifests itself. Plants 
grown from seeds out of one pod, and animals produced at 
one birth, are not alike ; and sometimes differ considerably. 
In a litter of pigs or of kittens, we rarely see uniformity of 
markings ; and occasionally, there are important structural 
contrasts. I have myself recently been shown a litter of 
Newfoundland puppies, some of which had four digits to 


their feet, while in others, there was present on each hind-foot, 
what is called the " dew-claw *' — a rudimentary fifth digit. 

Thus, induction points to three causes of variation, all in 
action together. We have heterogeneity among progenitors, 
which, did it act uniformly and alone in generating, by composi- 
tion of forces, new deyiations, would impress such new devia- 
tions to the same extent on all offitpring of the same parents ; 
which it does not. We have functional variation in the pa- 
rents, which, acting either alone or in combination with the pre- 
ceding cause, would entail like variations on all young ones 
simultaneously produced ; which it does not. And there is 
consequently some third cause of variation^ yet to be found, 
which acts along with the structural and functional variations 
of ancestors and parents. 

§ 87. Already, in the last section, there has been implied 
some relation between variation and the action of external 
conditions. The above-cited contrast, between the uniformity 
of wild species and the multiformity of the same species 
when cultivated or domesticated, thrusts this truth upon us. 
Respectiag the variations of plants, Mr Darwin remarks 
that " ^ sports' are extremely rare under nature, but far from 
rare under cultivation." Others who have studied the matter 
assert^ that if a species of plant which, up to a certain time, 
has maintained great uniformity, once has its constitution 
thoroughly disturbed, it will go on varying indefinitely. 
Though, in consequence of the remoteness of the periods at 
which they were domesticated, there is a lack of positive 
proof that our extremely variable domestic animals have be- 
come variable under the changed conditions implied by do- 
mestication, having been previously constant ; yet competent 
judges do not doubt that this has been the case. 

Now the constitutional disturbance which precedes varia- 
tion, can be nothing else than an overthrowing of the pre- 
established equilibrium of functions. Transferring a plant 
from forest lands to a ploughed field or a manured garden, is 


altering the balance of forces to which it has been hitherto 
subject ; by supplying it with different proportions of the 
assimilable matters it requires, and taking away some of the 
positive impediments to its growth which competing wild 
plants before offered. An animal taken from woods or plains, 
where it lived on wild food of its own procuring, and placed 
under restraint, while artificially supplied with food not quite 
like what it had before, is an animal subject to new outer ac- 
tions^ to which its inner actions must be re-adjusted. From 
the general law of equilibration we found it to follow, that 
" the maintenance of such a moving equilibrium '' as an or- 
ganism displays, ^' requires the habitual genesis of internal 
forces corresponding in number, directions, and amounts, to 
the external incident forces — as many inner functions, 
single or combined, as there are single or combined outer ac- 
tions to be met " {Firat Principles, § 133) ; and more recently 
(§ 27) > we have seen that Life itself is '^ the definite combin- 
ation of heterogeneous changes, both simultaneous and suc- 
cessive, in correspondence with external co-existences and 
sequences." Necessarily, therefore, an organism exposed to a 
permanent change in the arrangement of outer forces, must 
undergo a permanent change in the arrangement of inner 
forces. The old equilibrium must be destroyed ; and a new 
equilibrium must be established. There must be func- 
tional perturbations, ending in a re-adjusted balance of 

If, then, change of conditions is the only known cause by 
which the original homogeneity of a species is destroyed ; 
and if change of conditions can affect an organism only by 
altering its functions; it follows that alteration of func- 
tions is the only known internal cause to which the com- 
mencement of variation can be ascribed. That such minor 
functional changes as parents undergo from year to year, are 
influential on the offspring, we have seen to be proved by 
the greater unlikeness that exists between children bom to 
the same parents at different times, than exists between 


twins. And here we seem forced to conclude, that the larger 
functional variations produced by greater external changes, 
are the initiators of those structural variations which, when 
once commenced in a species, lead by their combinations and 
antagonisms to multiform results. Whether they are or 
are not the direct initiators, they must stiU be the indirect 

§ 88. That they are not in all cases, or even in most cases, 
the direct initiators, is clear. Were they so, those unlike- 
nesses which exist between plants that grow from seeds out 
of the same seed-vessel, or between animals belonging to the 
same litter, would be inexplicable. Here, all the antecedents, 
structural and functional, appear to be alike for each of the 
new organisms. Any deviations caused by structural con- 
trasts or functional disturbances in the parents, must be 
equally shared in by all simultaneously-produced offspring. 
Hence, an explanation of the variations arising under such 
conditions, has still to be sought. 

These are the variations termed " spontaneous." Not that 
those who apply to them this word or some equivalent, mean 
to imply that they are uncaused. Mr Darwin expressly 
guards himself against such an interpretation. He says : — 
" I have hitherto sometimes spoken as if the variations — so 
common and multiform in organic beings under domestica- 
tion, and in a lesser degi*ee in those in a state of nature — had 
been due to chance. This, of course, is a wholly incorrect 
expression, but it serves to acknowledge plainly our ignorance 
of the cause of each particular variation." Not only, how- 
ever, do I hold, in common with Mr Darwin, that there must 
be some cause for these apparently-spontaneous variations ; 
but it seems to me that a definite cause is assignable. I 
think it may be shown that unUkenesses must necessarily 
arido between the new individuals simultaneoasly produced 
by the same parents. Instead of the occurrence of such 


yariations being inexplicable, we shall presently see that the 
absence of them would be inexplicable. 

In any series of dependent changes, a small initial difference 
often works a marked difference in the results. The mode in 
which a particular breaker bursts on the beach, may determine 
whether the seed of some foreign plant which it bears, is oris not 
stranded — may cause the presence or absence of this plant from 
the Flora of the land; and may so affect, for millions of years, in 
countless ways, the living creatures throughout the land. A 
single touch, by introducing into the body some morbid mat- 
ter, may set up an immensely-involved set of functional dis- 
turbances and structural alterations. The whole tenor of a life 
may be changed by a word of advice ; or a glance may 
determine an action which alters thoughts, feelings, and 
deeds throughout a long series of years. In those still more 
involved combinations of changes which societies exhibit, 
this truth is still more conspicuous. A hair's-breadth differ- 
ence in the direction of some soldier's musket at the battle of 
Areola, by killing Napoleon, might have changed events 
throughout Europe : though the social organization in each 
European country, would have been now very much what it 
is, yet in countless details it would have been different. 

Illustrations like these, with which pages might be filled, 
prepare us for the conclusion, that organisms produced by 
the same parents at the same time, must be more or less 
differentiated both by insensible initial differences, and by 
slight differences in the conditions to which they are subject 
during their evolution. We need not, however, rest with 
assuming such initial differences : the necessity of them is 
demonstrable. The individual germ-cells which, in succes- 
sion or simultaneously, are separated from the same parent, 
can never be exactly alike ; nor can the sperm-cells which 
fertilize them. When treating of the instability of the 
homogeneous {First Principles, § 109), we saw that no two 
parts of any aggregate, can be similarly conditioned with 


respect to incident forces ; and that being subject to forces 
that are more or less unlike, they must become more or less 
unlike. Hence, no two ova in an ovarum or ovules in a 
seed-vessel— no two spermatozoa or pollen-cells, can be 
identical. Whether or not there arise other contrasts, there 
are certain to arise quantitative contrasts ; since the process 
of nutrition cannot be absolutely alike for all. The repro- 
ductive centres must begin to differentiate from the very 
outset. Such being the necessities of the case, what 

will happen on any successive or simultaneous fertilizations ? 
There wiU inevitably result more or less unlikeness between 
the combined parental influences in every instance. Quan- 
titative differences among the sperm-cells and among the 
germ-ceUs, will insure this. Grant that the number of 
physiological units contained in any one reproductive cell, can 
rarely if ever be exactly equal to the number contained 
in any other, ripened at the same time or at a different time ; 
and it follows that among the fertilized germs produced by 
the same parents, the physiological units derived from each 
parent will bear a different numerical ratio to each other in 
every case. If now the parents are constitutionally alike, 
that is, alike in the polarities of their physiological units, 
the variation in the ratio between the physiological units 
they severally bequeath to the fertilized germs, cannot cause 
unlikenesses among the offspring. But if otherwise, no two 
of the ofi&pring can be alike. In every case, the small initial 
difference in the proportions of the slightly-unlike units, 
will lead, during evolution, to a continual multiplication of 
differences : the insensible divergence at the outset, will gener- 
ate sensible divergences at the conclusion. Possi- 
bly some may hence infer, that though, in such case, the 
offspring must differ somewhat from each other and from 
both parents ; yet that in every one of them there must 
result a homogeneous mixture of the traits of the two parents. 
A little consideration shows that the reverse is inferable. If, 
throughout the process of development, the physiological 


units derived from each parent, preserved the same ratio to 
each other in all parts of the growing organism, each organ 
would show as much as every other, the influence of either 
parent. But we know, d priori, that no such uniform dis- 
tribution is possible. It has been shown (First PfHneiples, 
§ 123), that in any mixed aggregate of units, segregation 
must inevitably go on. Incident forces wiU tend ever to 
cause separation of the two orders of units from each other — 
will integrate groups of the one order in one place, and 
groups of the other order in another place. Hence there 
must arise, not a homogeneous mean between the two 
parents; but a mixture of organs, some of which mainly 
follow the one parent and some the other. And this is the 
kind of mixture which observation shows us. 

Still it may be fairly objected, that however the attributes 
of the two parents are variously mixed in their several 
offspring, they must in all the ofispring fall between the 
extremes displayed in the parents. In no characteristic 
could one of the young exceed both parents, were there no 
cause of " spontaneous vamtion " but the one alleged. Evi- 
dently, then, there is a cause yet unfound. 

§ 89. Thus far we have contemplated the process under 
its simplest aspect. While we have assumed the two parents 
to be somewhat unlike, we have assumed that each parent 
has a homogeneous constitution — ^is built up of physiologi- 
cal units that are exactly alike. But in no case can such a 
homogeneity exist. Each parent had parents that were more 
or less contrasted — each parent inherited at least two orders 
of physiological units, not quite identical. Here then we 
have a further cause of variation. The sperm-cells or germ- 
ceUs which any organism produces, will difier from each 
other not quantitatively only, but qualitatively. Of the 
slightly-unlike physiological units bequeathed to an organism, 
its reproductive cells cannot habitually contain the same pro- 
portions ; and we may expect the proportions to vary not 


slightly but greatly. Just as, during the evolution of an or- 
ganism, the physiological units derived from the two parents 
tend to segregate, and produce likeness to the male parent in 
this feature and to the female parent in that ; so, during the 
formation of reproductive cells by such organism, there will 
arise in one cell a predominance of the physiological units 
derived from one parent, and in another cell a predominance 
of the physiological units derived from the other parent. The 
instability of the homogeneous forbids us to assume an even 
distribution of the two orders of units in all the reproductive 
cells. And inequalities once arising among them, must tend 
ever to become more marked ; since, wherever units of a 
given order have begun to segregate, the process of differenti- 
ation and integration tends to segregate them more and more. 
Thus, then, every fertilized germ, besides containing different 
amounts of the two parental influences, will contain different 
kinds of influences — ^this having received a marked impress 
from one maternal or paternal ancestor, and that from an- 

Here, then, we have a clue to the multiplied variations, and 
sometimes extreme variations, that arise in races which have 
once begun to vary. Amid countless different combinations 
of units derived from parents, and through them from ances- 
tors, immediate and remote — amid the various conflicts in 
their slightly-different polarities, opposing and conspiring 
with each other in all ways and degrees ; there will from 
time to time arise special proportions causing special devi- 
ations. From the general law of probabilities it is inferable, 
that while these involved influences, derived from many pro- 
genitors, must, on the average of cases, obscure and partially 
neutralize one another ; there must occasionally result such 
combinations of them as will produce considerable divergences 
from average structures ; and at rare intervals, such com- 
binations as will produce very marked divergences. There is 
thus a correspondence between the inferable results, and the 
results as habitually witnessed. 


§ 90. Still there remains a difficulty. It may be said that 
admitting functional change to be the initiator of variation 
— granting that the physiological units of an organism, 
modified by long subjection to new conditions, will tend to be- 
come modified in such way as to cause change of structure in 
oflfepring ; yet there will still be no cause of the supposed 
heterogeneity among the physiological units of different in- 
dividuals. There seems validity in the objection, that as all 
the members of a species whose circumstances have been al- 
tered, will be affected in the same manner, the results, when 
they begin to show themselves in descendants, will show them- 
selves in the same manner : not multiform variations will 
arise, but deviations all in one direction. 

The reply is simple. The members of a species thus cir- 
cumstanced, will not be similarly affected. In the absence of 
absolute uniformity among them, the functional changes 
caused in them will be more or less dissimilar. Just as men 
of slightly-unlike dispositions behave in quite opposite ways 
under the same circumstances ; or just as men of slightly- 
unlike constitutions get diverse disorders from the same 
cause, and are diversely acted on by the same medicine ; so, 
the insensibly-differentiated members of a species whose con- 
ditions have been changed, may at once begin to undergo 
various kinds of functional changes. As we have already 
seen, small initial contrasts may lead to large terminal con- 
trasts. The intenser cold of the climate into which a species 
has migrated, may cause in one individual increased con- 
sumption of food, to balance the greater loss of heat ; while 
in another individual, the new requirement may be met by a 
thicker growth of fur. Or, when meeting with the new foods 
which the new region furnishes, mere accident may deter- 
mine one member of the species to begin with one kind and 
another member with another kind ; and hence may arise 
established habits in these respective members and their 
descendants. Now when the functional divergences thus set 
up in sundry families of a species, have lasted long enough 


to affect their constitutions profoundly, and to modify some- 
what the physiological units thrown off in their reproductiye 
ceUs, the divergences produced by these in offipring, will be 
of diverse kinds. And the original homogeneity of constitu- 
tion having been thus destroyed, variation may go on with 
increasing facility. There will result a heterogeneous mix- 
ture of modifications of structure, caused by modifications of 
function ; and of still more numerous correlated modifica- 
tions, indirectiy so caused. By natural selection of the most 
divergent forms, the unlikenesses of parents will grow more 
marked, and the limits of variation wider. Until at length 
the divergences of constitutions and modes of life, become 
great enough to lead to segregation of the varieties. 

§ 91. That variations must occur, and that they must ever 
tend, both directly and indirectly, towards adaptive modifica- 
tions, are conclusions deducible from first principles ; apart 
from any detailed interpretations like the above. That the 
state of homogeneity is an unstable state, we have found to 
be a imiversal truth. Each species must pass from the uni- 
form into the more or less multiform, unless the incidence of 
external farces is exactly the same for all its members ; which 
it never can be. Through the process of differentiation and 
integration, which of necessity brings together, or keeps to- 
gether, like individuals, and separates unlike ones from them, 
there must nevertheless be maintained a tolerably uniform 
species ; so long as there continues a tolerably uniform set of 
conditions in which it may exist. But if the conditions 
change, either absolutely by some disturbance of the habitat, 
or relatively by spread of the species into other habitats, then 
the divergent individuals that result, must be segregated 
by the divergent sets of conditions into distinct varieties 
{First Principles, § 126). When, instead of contemplating 
a species in the aggregate, we confine our attention to a 
single member and its descendants, we see it to be a corollary 
from the general law of equilibration^ that the moving equili- 


brium constituted by the vital actions in each member of 
this family, must remain constant so long a£ the external ac- 
tions to which they correspond remain constant ; and that if 
the external actions are changed, the disturbed balance- of 
internal changes, if not overthrown, cannot oease undergoing 
modification until the internal changes are again in equiU- 
brium with the external actions: corresponding structural 
alterations having arisen. 

Or passing from these derivative laws to the ultimate law, 
we see that Variation is necessitated by the persistence offeree. 
The members of a species inhabiting any area, cannot be subject 
to like aggregates of forces over the whole of that area. And 
if, in different parts of the area, different kinds or amoimts or 
combinations of forces act on them, they cannot but become 
different in themselves and in their progeny. To say otherwise, 
is to say that differences in the forces will not produce differ- 
ences in the effects ; which is to deny the persistence of force. 

Whence it is also manifest, that there can be no variation 
of structure, but what is directly or indirectly consequent on 
variation of function. On the one hand, organisms in com- 
plete equilibrium with their conditions, cannot be changed 
except by change in their conditions ; since, to assert other- 
wise, is to assert that there can be an effect without a cause ; 
which is to deny the persistence of force. On the other hand, 
any change of conditions can affect an organism only by 
changing the actions going on in it — only b}' altering its func- 
tions* The alterations of functions being necessarily towards 
a re-establishment of the equilibrium, (for if not, the equili- 
brium must be destroyed and the life cease, either in the in- 
dividual or in descendants,) it follows that the structural alter- 
ations directly caused, are adaptations ; and that the correlated 
structural alterations indirectly caused, are the concomitants of 
adaptations. Hence, though, by the intercourse of organisms 
that have been functionally and structurally modified in dif- 
ferent directions, there may result organisms that deviate in 
compound ways which appear unrelated to external condi- 


tions, the deviations of such organisms must still be regarded 
as indirect results of functional adaptations. We must say 
that in all cases^ adaptive change of function is the primary 
and ever-acting cause of that change of structure which con- 
stitutes variation ; and that the variation which appears to 
be '' spontaneous/' is derivative and secondary. 



§ 92. A QUESTION raised, and hypothetically answered, in 
§§ 78 and 79, was there postponed until we had dealt with the 
topics of Heredity and Variation. Let us now resume the 
consideration of this question, in connexion with sundry 
others which the facts suggest. 

After contemplating the several methods by which the 
multiplication of organisms is carried on — after ranging 
them under the two heads of Homogenesis, in which the suc- 
cessive generations are similarly produced, and Heterogenesis, 
in which they are dissimilarly produced — after observing 
that Homogenesis is always sexual genesis, while Heteroge- 
nesis is asexual genesis with occasionally-recurring sexual 
genesis ; we came to the questions — why is it that some or- 
ganisms multiply in the one way, and some in the other P 
and why is it that where agamogenesis prevails, it is usually, 
from time to time, interrupted by gamogenesis ? In seeking 
an answer to this question, we inquired whether there are, 
common to both Homogenesis and Heterogenesis, any condi- 
tions under which alone sperm-cells and germ-cells arise and 
are united, for the production of new organisms; and we 
reached the conclusion that, in all cases, they arise only 
when there is an approach to equilibrium between the forces 
which produce growth and the forces which oppose growth. 
This answer to the question — when does gamogenesis recur P 



still left unanswered the question — why does gamogenesis 
recur P And to this the reply suggested was, that the ap- 
proach towards general equilibrium in organisms, "is ac- 
companied by an approach towards molecular equilibrium in 
them ; and that the need for this union of sperm-cell and 
germ-cell, is the need for overthrowing this equilibrium, and 
re-establishing active molecular change in the detached germ 
— a result which is probably effected by mixing the slightly- 
different physiological units of slightly-different individuals." 
This is the hypothesis which we have now to consider. Let 
us first look at the evidences which certain inorganic pheno- 
mena furnish. 

The molecules of any aggregate which have not a balanced 
arrangement, inevitably tend towards a balanced arrangement. 
As before mentioned {First Principles^ S 103) amorphous 
wrought iron, when subject to continuous jar, begins to arrange 
itself into crystals — its atoms assume a condition of polar 
equilibrium. The particles of unannealed glass, which are so 
unstably arranged that slight disturbing forces make them 
separate into small groups, take advantage of that greater 
freedom of movement given by a raised temperature, to ad- 
just themselves into a state of relative rest. During any 
such re-arrangement, the aggregate exercises a coercive force 
over its units. Just as in a growing crystal, the atoms suc- 
cessively assimilated from the solution, are made by the al- 
ready-crystallized atoms to take a certain form, and even to 
re-complete that form when it is broken ; so in any mass of 
imstably-arranged atoms that passes into a stable arrangement, 
each atom conforms to the forces exercised on it by all the 
other atoms. This is a corollary from the general law of 
equilibration. We saw {First Principles, § 130) that every 
change is towards equilibrium ; and that change can never 
cease until equilibrium is reached. Organisms, above 

all other aggregates, conspicuously display this progressive 
equilibration ; because their units are of such kinds, and so 
conditioned, as to admit of easy re-arrangementj Those 


extremely actiye changes which go on during the early 
stages of evolution, imply an immense excess of the mole- 
cular forces over those antagonist forces which the aggregate 
exercises on the molecules. While this excess continues, it 
is expended in growth, development, and function — expend!* 
ture for any of these purposes, being proof that part of the 
force embodied in molecular tensions, remains unbalanced. 
Eventually, however, this excess diminishes. Either, as in 
organisms which do not expend much force, decrease of assi- 
milation leads to its decline ; or, as in organisms which ex- 
pend much force, it is counterbalanced by the rapidly-increas- 
ing re-actions of the aggregate (§ 46). The cessation of 
growth, when followed, as in some organisms, by death, im- 
plies the arrival at an equilibrium between the molecular 
forces, and those forces which the aggregate opposes to them. 
When, as in other organisms, growth ends in the establish- 
ment of a moving equilibrium, there is implied such a de- 
creased preponderance of the molecular forces, as leaves no 
surplus beyond that which is used up in functions. The de- 
clining functional activity, characteristic of advancing life, 
expresses a further decline in this surplus. And when all 
vital movements come to an end, the implication is, that 
the actions of the units on the aggregate and the re- 
actions of the aggregate on the units, are completely bal- 
anced. Hence, while a state of rapid growth indi- 
cates such a play of forces among the units of an aggregate, 
as will produce active re-distribution; the diminution and 
arrest of growth, shows that the units have fallen into such 
relative positions that re-distribution is no longer so facile. 
When, therefore, we see that gamogenesis recurs only when 
growth is decreasing, or has come to an end, we must say 
that it recurs only when the organic units are approxima- 
ting to equilibrium — only when their mutual restraints pre,- 
vent them from readily changing their arrangements in obe- 
dience to incident forces. 

That units of like forms can be built up into a more stable 

18 ♦ 


aggregate than units of slightly unlike forms, is tolerably 
manifest, a priori. And we have facts which prove that mixing 
allied but somewhat different units^£^&8 lead to comparative in* 
stability. Most metallic alloys exemplify this truth. Com- 
mon solder, which is a mixture of lead and tin, melts at a much 
lower temperature than either lead or tin. The compound of 
lead, tin, and bismuth^ called " fusible metal," becomes fluid 
at the temperature of boiling water ; while the temperatures 
at which lead, tin, and bismuth become fluid, are, respectively, 
612^ 442°, and 497% F. Still more remarkable is the illustra- 
tion furnished by potassium and sodium. These metals are 
very near akin in all respects — in their specific gravities, their 
atomic weights, their chemical affinities, and the properties 
of their compounds. That is to say, all the evidences unite to 
show that their units, though not identical, have a close resem* 
blance. What now happens when they are mixed ? Potassium 
alone melts at 136°, sodium alone melts at 190°, but the alloy of 
potassium and sodium, is liquid at the ordinary temperature of 
the air. Observe the meaning of these facts, expressed in 
general terms. The maintenance of a solid form by any group 
of units, implies among them an arrangement so stable, that 
it cannot be overthrown by the incident forces. Whereas the 
assumption of a liquid form, implies that the incident forces 
suffice to destroy the arrangement of the units. In the one 
case^ the thermal undulations fail to dislocate the parts ; while 
in the other case, the parts are so dislocated by the thermal 
undulations, that they fall into total disorder — a disorder 
admitting of easy re-arrangement into any other order. For 
the liquid state is a state in which the units become so far free 
from mutual restraints, that incident forces can change their 
relative positions very readily. Thus we have reason to 
conclude, that an aggregate of units which, though in the 
main similar to each other, have minor differences, must be 
more unstable than an aggregate of homogeneous units : the 
one will yield to disturbing forces which the other successfully 


Now though the colloidal atoms of which organisms are 
mainly built, are themselves highly composite ; and though 
the physiological units compounded out of these colloidal 
atoms, must have structures far more involved ; yet it must 
happen with such units, as with simple units, that those 
which have exactly like forms, will admit of arrangement into 
a more stable aggregate than those which have slightly- 
unlike forms. Among units of this order, as among units 
of a simpler order, imperfect similarity must entail imperfect 
polar balance, and consequent diminished ability to withstand 
disturbing forces. Hence, given two organisms which, by 
diminished nutrition or increased expenditure, are being ar- 
rested in their growths — given in each an approaching 
equilibrium between the forces of the units and the forces of 
the aggregate — given, that is, such a comparatively-balanced 
state among the units, that re-arrangement of them by inci- 
dent forces is no longer so easy ; and it will follow that by 
uniting a group of units from the one organism with a group 
of slightly-different units from the other, the tendency to- 
wards equilibrium will be diminished, and the mixed units 
will be rendered more modifiable in their arrangements by 
the forces acting on them : they will be so far freed as to be- 
come again capable of that re-distribution which constitutes 
evolution. This view of the matter is in harmony 

with the results of observation on the initial stages of develop- 
ment. Some pages back, it was asserted that sperm-cell and 
germ- cell severally arrive, before their union, at a condition 
of equilibrium. Though approximately true, this is not liter- 
ally true. I learn from Dr W. H. Eansom, who has investi- 
gated the question with great care, that the unfertilized ovum 
continues, for a time, to undergo changes similar to those which 
the fertilized ovum undergoes; but that these changes, becoming 
languid and incomplete, are finally arrested by decomposition. 
Here we find what might be expected. In the first place, an 
organism which develops germ-cells, is not in a state of mole- 
cular equilibrium, but in a state of approach to such equili- 


briiim. Hence, a group of physiological units cast off from it, 
will not be wholly without a tendency to undergo the struc- 
tural re-arrangements which we call development ; but will 
have this tendency unduly restrained by partially-balanced 
polarities. In the second place, undue restraint of the phy- 
siological units, while it renders them as wholes less-easily 
altered in their relative positions by incident forces, thereby 
also renders them more liable to be individually decomposed 
by incident forces : the same thermal undulations which, if 
the physiological units are comparatively free, will aid their 
re-arrangement by giving them still greater freedom, will, if 
they are comparatively fixed, begin to change the arrange- 
ments of their components — will decompose them. In the 
third place, their decomposition will be prevented as well as 
their re-distribution facilitated, by such disturbance of their 
polarities as we have seen must result from mixing with them 
the slightly-unlike units of another organism. 

And now let us test this hypothesis, by seeing what power 
it gives us of interpreting established inductions. 

§ 93. The majority of plants being hermaphrodites, it has, 
until quite recently, been supposed that the ovules of each 
flower are fertilized by pollen from the anthers of the same 
flower. Mr Darwin, however, has shown that the arrange- 
ments are generally auoh as to prevent this : either the ovules 
and the pollen are not ripe simultaneously, or obstacles pre- 
vent access of tl^ one to the other. At the same time, he has 
shown that there exist arrangements, often of a remarkable 
kind, which facilitate the transfer of pollen by insects from the 
stamens of one flower to the pistil of another. Simi- 

larly, it has been found that among the lower animals, herma- 
phrodism does not usually involve the production of fertile 
germs, by the union of sperm-cells and germ-cells developed 
m the same individual ; but that the reproductive centres of 
one individual are imited with those of another, to produce 
fertile germs. Either, as in the Pyrosoma, the Perophora, and 


in many higher mollnscs, the ova and spermatozoa are ma- 
tured at different times ; or, as in annelids, they are prevented 
by their relative positions from coming in contact. 

Remembering the fact that among the higher classes of 
organisms, fertilissation is always effected by combining the 
sperm-cell of one individual with the germ-cell of another ; 
and joining with it the fact that among hermaphrodite organ- 
isms, the germ-cells developed in any individual, are usually 
not fertilized by sperm-cells developed in the same individual ; 
we see reason for thinking that the essential thing in fertiliz- 
ation, is the union of specially -fitted portions of different or- 
ganisms. If fertilization depended on the peculiar properties 
of sperm-cell and germ-cell, as such ; then, in hermaphrodite 
organisms, it would be a matter of indifference whether the 
united sperm-cells and germ-cells were those of the same in- 
dividual, or those of different individuals. But the circum- 
stance that there exist in such organisms, elaborate ap- 
pliances for mutual fertilization, shows that unlikeness of 
derivation in the united reproductive centres, is the deside- 
ratum. Now this is just what th<a foregoing hypothesis 
implies. If, as was concluded, fertilization has for its object 
the disturbance of that approximate equilibrium existing 
among the physiological units separated from an adult organ- 
ism ; and if, as we saw reason to think, this object is effected 
by mixture with the slightly-different physiological units of 
another organism ; then, we at the same time see reason to 
think, that this object will not be effected by mixture with 
physiological units belonging to the same organism. Thus, 
the hypothesis leads ujs to expect such provisions as we find 

§ 94. But here a difficulty presents itself. These proposi- 
tions seem to involve the conclusion, that self-fertilization is 
impossible. It apparently follows from them, that a group of 
physiological units from one part of an organism, ought to 
have no power of altering the state of approaching balance in 


a group from another part of it. Yet self-fertilization does 
occur. Though the ovules of one plant, are generally fer- 
tilized by pollen from another plant of the same kind ; yet 
they may be, some of them, fertilized by the pollen of the same 
plant. And though, among hermaphrodite animals, self-fer- 
tilization is usually negatived by structural or functional ar- 
rangements ; yet in certain Entozoa, there appear to be special 
provisions by which the sperm-cells and germ-cells of the same 
individual may be united, when not previously united with . 
those of another individual. Certainly, at first sight, these 
facts do not consist with the above supposition. Neverthe- 
less, there is a satisfactory solution of them. 

In the last chapter, when considering the variations that 
may result in offspring from the combination of unlike 
parental constitutions, it was pointed out that in an unfolding 
organism, composed of slightly-different physiological units 
derived from slightly-different parents, there cannot be main- 
tained an even distribution of the two orders of units. We 
saw that the instability of the homogeneous, negatives the 
uniform blending of them ; and that, by the process of differ- 
entiation and integration, they must be more or less separated ; 
so that in one part of the body the influence of one parent will 
predominate, and in another part of the body the influence of 
the other parent : an inference which harmonizes with daily 
observation. And we cdso saw, that the sperm-cells or germ- 
cells produced by such an organism, must, in virtue of these 
same laws, be more or less unlike one another. It was shown 
that through segregation, some of the sperm-cells or germ- 
ceUs will get an excess of the physiological units derived 
from one side, and some of them an excess of those derived 
from the other side : a cause which accounts for the unlikenesses 
among o&pring simultaneously produced. Now from this 
segregation of the different orders of physiological units, in- 
herited from different parents and lines of ancestry, there 
arises the possibility of self-fertilization in hermaphrodite 
organisms. If the physiological units contained in the sperm- 


cells and germ-cells of the same flower, are not quite homo- 
geneous — if in some of the ovules the physiological units 
derived from the one parent greatly predominate, and in some 
of the ovules those derived from the other parent ; and if the 
like is true of the poUen-cells ; then, some of the ovules may 
be nearly as much contrasted with some of the pollen-cells, in 
the characters of their contained units, as were the ovules and 
pollen-cells of the parents from which the plant proceeded. 
Between part of the sperm-cells and part of the germ-cells, the 
community of nature will be such that fertilization will not 
result from their union ; but between some of them, the 
differences of constitution will be such that their union 
will produce the requisite molecular instability. The facts, 
so far as they are known, seem in harmony with this deduction. 
Self-fertilization in flowers, when it takes place, is not so 
efficient as mutual fertilization. Though some of the ovules 
produce seeds, yet more of them than usual are abortive. 
From which, indeed, results the establishment of varieties that 
have structures favourable to mutual fertilization; since, being 
more prolific, these have, other things equal, greater chances 
in the " struggle for existence." 

Further evidence is at hand in support of this interpreta- 
tion. There is reason to believe that self-fertilization, which 
at the best is comparatively inefficient, loses all efficiency in 
course of time. After giving an account of the provisions for 
an occasional, or a frequent, or a constant crossing between 
flowers ; and after quoting Prof. Huxley to the effect that 
among hermaphrodite animals, there is no case in which " the 
occasional influence of a distinct individual can be shown to 
be phj'^sically impossible ; '* Mr Darwin writes — " from these 
several considerations and from the many special facta which 
I have collected, but which I am not here able to give, I am 
strongly inclined to suspect that, both in the vegetable and 
animal kingdoms, an occasional intercross with a distinct in- 
dividual is a law of nature. * * * in none, as I suspect, 
can self-fertilization go on for perpetuity." This conclusion, 


based wholly on observed facts, is just the conclusion to which 
the foregoing argument points. That necessary action and 
the re-action between the parts of an organism and the 
organism as a whole — that power of the aggregate to re-mould 
the units, which is the correlative of the power of the units to 
build up into such an aggregate ; implies that any differences 
existing between the units inherited by an organism, must 
gradually diminish. Being subject in common to the total 
forces of the organism, they will in common be modified to- 
wards congruity with these forces; and therefore towards 
likeness with each other. If, then, in a self-fertilizing organion 
and its self-fertilizing descendants, such contrasts as origin- 
ally existed among the physiological units, are progressive- 
ly obliterated — if, consequently, there can no longer be a 
segregation of different physiological units in different sperm- 
cells and germ-cells ; self-fertilization will become impossible : 
step by step the fertility will diminish, and the series will 
finally die out. 

And now observe, in confirmation of this view, that self- 
fertilization is limited to organisms in which an approximate 
equilibrium among the organic forces, is not long maintained. 
While growth is actively going on, and the physiological units 
are sutject to a continually-changing distribution of forces, 
no decided assimilation of the units can be expected : like 
forces acting on the unlike units, will tend to segregate them, 
so long as continuance of evolution permits further segrega- 
tion ; and only when further segregation cannot go on, will 
the like forces tend to assimilate the units. Hence, where 
there is no prolonged maintenance of an approximate organic 
balance, self-fertilization may be possible for some gener- 
ations ; but it will be impossible in organisms distinguished 
by a sustained moving equilibrium. 

% 95. The interpretation which it affords of sundry pheno- 
mena familiar to breeders of animals, adds probability to the 
hypothesis. Mr Darwin has collected a large " body of facts, 


showing, in accordance with the almost universal belief of 
breeders, that with animals and plants a cross between different 
varieties, or between individuals of the same variety but of 
another strain, gives vigour and fertility to the offspring ; and 
on the other hand, that close interbreeding diminishes vigour 
and fertility," — a conclusion harmonizing with the current 
belief respecting family-intermarriages in the human race. 
Have we not here a solution of these facts P Relations must, on 
the average of cases, be individuals whose physiological units 
are more nearly alike than usual. Animals of different 
varieties must be those whose physiological units are more 
unlike than usual. In the one case, the unlikeness of the 
units may frequently be insufficient to produce fertilization ; 
or, if sufficient to produce fertilization, not sufficient to produce 
that active molecular change required for vigorous develop- 
ment. In the other case, both fertilization and vigorous 
development will be made probable. 

"Not are we without a cause for the irregular manifestation of 
these general tendencies* The mixed physiological units com- 
posing any organism, being, as we have seen, more or less se- 
gregated in the reproductive centres it throws off; there may 
arise various residts, according to the degrees of difference 
among the units, and the degrees in which the units are segre- 
gated. Of two cousins who have married, the common grand- 
parents may have had either similar or dissimilar constitu- 
tions ; and if their constitutions were dissimilar, the probability 
that their married grandchildren will have offspring will be 
greater than if their constitutions were similar. Or the 
brothers and sisters from whom these cousins descended, in- 
stead of severally inheriting the constitutions of Uieir parents 
in tolerably equal degrees, may have sevoraUy inherited them 
in very diflferent degrees : in which last case, intermarriages 
among the grandchildren will be less likely to prove infertile. 
Or the brothers and sisters from whom these cousins de- 
scended, may severally have married persons very like, or 
very imlike, themselves; and from this cause there may 


have resulted^ either an undue likeness, or a due unlike- 
ness, between the married cousins. These several causes, 
conspiring and conflicting in endless ways and degrees, will 
work multiform effects. Moreover, differences of segrega- 
tion will make the reproductive centres produced by the 
same nearly-related organisms, vary considerably in their 
amounts of unlikeness ; and therefore, supposing their amounts 
of unlikeness great enough to cause fertilization, this fertiliza- 
tion will be effective in various degrees. Hence it may happen 
that among offspring of nearly-related parents, there may be 
some in which the want of vigour is not marked, and others in 
which there is decided want of vigour. So that we are alike 
shown why in-and-in breeding tends to diminish both fertility 
and vigour ; and why the effect cannot be a uniform effect, but 
only an average effect. 

§ 96. While, if the foregoing arguments are valid, gamo- 
genesis has for its main end, the initiation of a new develop- 
ment by the overthrow of that approximate equilibrium arrived 
at among the molecules of the parent-organisms ; a further end 
appears to be subserved by it. Those inferior organisms 
which habitually multiply by agamogenesis, have conditions 
of life that are simple and uniform ; while those organisms 
that have highly-complex and variable conditions of life, 
habitually multiply by gamogenesis. Now if a species has 
complex and variable conditions of life, its members must be 
severally exposed to sets of conditions that are slightly 
different : the aggregates of incident forces cannot be alike 
for all the scattered individuals. Hence, as functional 
deviation must ever be inducing structural deviation, each 
individual throughout the area occupied, tends to become 
fitted for the particular habits which its particular conditions 
necessitate ; and in so far, unfitted for the average habits 
proper to the species. But these undue specializations are 
continually checked by gamogenesis. As Mr Darwin remarks 
— " intercrossing plays a very important part in nature in 


keeping the individuals of the same species, or of the yariety, 
true and uniform in character :" the idiosyncratic divergences 
obliterate each other. Gamogenesis, then, is a means of 
turning to positive advantage, the individual differentiations 
which, in its absence, would result in positive disadvantage. 
Were it not that individuals are ever being made unlike each 
other by their unlike conditions, there would not arise among 
them those contrasts of molecular constitution, which we have 
seen to be needful for producing the fertilized germs of new 
individuals. And were not these individual differentiations 
ever being mutually cancelled, they would end in a fatal 
narrowness of adaptation. 

This truth will be most clearly seen if we reduce it to its 
purely abstract form, thus : — Suppose a quite homogeneous 
species, placed in quite homogeneous conditions ; and suppose 
the constitutions of all its members in complete concord with 
their absolutely-uniform and constant conditions; what must 
happen P The species, individually and collectively, is in a 
state of perfect moving equilibrium. All disturbing forces 
have been eliminated. There remains no force which can, in 
any way, change the state of this moving equilibrium ; either 
in the species as a whole or in its members. But we have 
seen {First Principles, § 133) that a moving equilibrium is but 
a transition towards complete equilibration, or death. The 
absence of differential or un-equilibrated forces among the 
members of a species, is the absence of all forces that can 
cause changes in the conditions of its members — ^is the ab- 
sence of all forces which can initiate new organisms. To say, 
as above, that complete molecular homogeneity existing 
among the members of a species, must render impossible that 
mutual molecular disturbance which constitutes fertilization, 
is but another way of saying, that the actions and re-actions 
of each organism, being in perfect balance with the actions 
and re-actions of the environment upon it, there remains in 
each organism, no force by which it differs from any other 
— ^no force which any other does not meet with an exactly 


equal foroe-^no force which can set up a new evolution 
among the unite of any other. 

And so we reach the remarkable conclusion, that the life of 
a species, like the life of an individual, is maintained by the 
unequal and ever* varying actions of incident forces on its 
different parts. An individual homogeneous throughout, and 
having its substance everywhere continuously subject to like 
actions, could undergo none of those changes which life con- 
sists of; and similarly, an absolutely-uniform species, having all 
its members exposed to identical influences, would be deprived 
of that initiator of change which maintains its existence as 
a species. Just as, in each organism, incident foroes constantly 
produce divergences from the mean state in various directions, 
which are constantly balanced by opposite divergences indi- 
rectly produced by other incident foroes; and just as the 
combination of rhythmical functions thus maintained, consti- 
tutes the life of the organism ; so, in a species, there is, through 
gamogenesis, a perpetual neutralization of those contrary de- 
viations from the mean state, which are caused in its different 
parts by different sets of incident forces ; and it is similarly 
by the rhythmical production and compensation of these con- 
trary deviations, that the species continues to live. The 
moving equilibrium in a species, like the moving equilibrium 
in an individual, would rapidly end in complete equilibration, 
or death, were not its continually-dissipated foroes continually 
re-supplied from without. Besides owing to the external 
world, those energies which, from moment to moment, keep 
up the lives of its individual members ; every species owes 
to certain more indirect actions of the external world, those 
energies which enable it to perpetuate itself in successive 

§ 97. What evidence still remains, may be conveniently 
woven up along with a recapitulation of the argument pursued 
through the last three chapters. Let us contemplate the facts 
in their synthetic order. 


That compounding and re-compounding through which wo 
pass from the simplest inorganic substances to the most com-^ 
plez organic substances, has several concomitants. Each 
successive stage of composition, presents us with atoms that are 
severally larger or more integrated, that are severally more 
heterogeneous, that are severally more unstable, and that are 
more numerous in their kinds (Firat Principles, § 111). And 
when we come to the substances of which living bodies are 
formed, we find ourselves among multiplied, divergent groups 
and sub-groups of compounds, the units of which are large, 
heterogeneous, and unstable, in high degrees. There is no 
reason to assume that this process ends with the formation of 
those complex colloids which characterize organic matter. A 
more probable assumption is, that out of the complex colloidal 
atoms, there are evolved, by a still further integration, atoms 
that are stiU more heterogeneous, and of kinds that are still 
more multitudinous. What must be their properties P Al- 
ready the colloidal atoms are extremely unstable— capable 
of being variously modified in their characters by very slight 
incident forces ; and already the complexity of their polarities 
prevents them from readily falling into those positions of 
polar equilibrium which result in crystallization. Now the 
organic atoms composed of these colloidal atoms, must be simi- 
larly characterized in far higher degrees. Far more numerous 
must be the minute changes that can be wrought in them by 
minute external forces ; far more free must they remain for a 
long time to obey forces tending to re-distribute them ; and 
far greater must be the number of their kinds. 

Setting out with these physiological units, the existence of 
which various organic phenomena compel us to recognize, and 
the production of which the general law of Evolution thus 
leads us to anticipate ; we get an insight into the phenomena 
of Genesis, Heredity, and Variation. If each organism is built 
of certain of these highly-plastic units peculiar to its species 
— units which slowly work towards an equilibrium of their 
complex polarities, in producing an aggregate of the specific 


structure, and which are at the same time slowly modifiable 
by the re-actions of this aggregate — we see why the mul- 
tiplication of organisms proceeds in the several ways, and 
with the various results, which naturalists have observed. 

Heredity, as shown not only in the repetition of the specific 
structure, but in the repetition of ancestral deviations from it, 
becomes a matter of course ; and it falls into unison with the 
fact that^ in various simple organisms, lost parts can be re- 
placed, and that, in still simpler organisms^ a fragment can 
develop into a whole. 

While an aggregate of physiological units continues to 
grow^ by the assimilation of matter which it moulds into 
other units of like type ; and while it continues to undergo 
changes of structure ; no equilibrium can be arrived at between 
the whole and its parts. Under these conditions, then, an 
un-difierentiated portion of the aggregate— a group of phy- 
siological units not bound up into a specialized tissue — ^will 
be able to arrange itself into the structure peculiar to the 
species ; and will so arrange itself, if freed from controlling 
forces, and placed in fit conditions of nutrition and temper- 
ature. Hence the continuance of agamogenesis in little-differ- 
entiated organisms, so long as assimilation continues to be 
greatly in excess of expenditure. 

But let growth be checked and development approach its 
completion — let the units of the aggregate be severally exposed 
to an almost constant distribution of forces ; and they must 
begin to equilibrate themselves. Arranged as they will 
gradually be, into comparatively stable attitudes in relation 
to each other, their mobility will diminish ; and groups of 
them, partially or wholly detached, will no longer readily re- 
arrange themselves into the specific form. Agamogenesis will 
be no longer possible ; or, if possible, will be no longer easy. 

When we remember that the force which keeps the Earth 
in its orbit, is the gravitation of each particle in the Earth 
towards every one of the group of particles existing 91,000,000 
of miles off; we cannot reasonably doubt, that each unit in 


an organism, acts, by its polar forces, on all the other units, 
and is re-acted on by them. When, too, we learn that 
glass has its molecular constitution changed by light, and 
that substances so rigid and stable as metals, have their 
atoms re-arranged by forces radiated in the dark from 
adjacent objects ; we are obliged to conclude that the ex- 
cessively-unstable units of which organisms are built, must be 
sensitive in a transcendant degree, to all the forces pervading 
the organisms composed of them — ^must be tending ever to 
re-adjust, not only their relative positions, but their molecular 
structures, into equilibrium with these forces. Hence, if ag- 
gregates of the same species are differently conditioned, and 
re-act differently on their component units, their component 
units will be rendered somewhat different; and they will 
become the more different the more widely the re-actions 
of the aggregates upon them differ, and the greater the num- 
ber of generations through which these different re-actions of 
the aggregates upon them are continued. 

If, then, unlikenesses of function among individuals of the 
same species, produce unlikenesses between the physiological 
units of one individual and those of another ; it becomes com- 
prehensible that when groups of units derived from two indi- 
viduals are united, the group formed will be more unstable 
than either of the groups was before their union : the mixed 
units will be less able to resist those re-distributing forces 
which cause evolution ; and may so have restored to them, 
the capacity for development which they had lost. 

This view harmonizes with the conclusion which we saw 
reason to draw, that fertilization does not depend on any 
intrinsic peculiarities of sperm-cells and germ-cells ; but 
depends on their derivation from different individuals. It 
explains the fact that nearly-related individuals are less 
likely to have offspring than others ; and that their offspring, 
when they have them, are frequently feeble. And it gives 
us a key to the converse fact, that the crossing of varieties 
results in unusual fertility and vigour. 



Bearing in mind that the slightly-different orders of phy- 
siological units which an organism inherits from its parents, 
are subject to the same set of forces; and that when the 
organism is fully developed, this set of forces, becoming con- 
stant, tends slowly to re-mould the two orders of units into 
the same form ; we see how it happens that self-fertilization 
becomes impossible in the higher organisms, while it remains 
possible in the lower organisms. In long-lived creatures that 
have tolerably-definite limits of growth, this assimilation of 
the somewhat-unlike physiological xmits, is liable to go on to 
an appreciable extent ; whereas in organisms which do not 
continuously subject their component units to constant forces, 
there will be much less of this assimilation. And where the 
assimilation is not considerable, the segregation of mixed 
units, may cause the sperm-cells and germ-cells developed in 
the same individual, to be sufficiently different to produce, by 
their union, fertile germs ; and several generations of self- 
fertilizing descendants may succeed one another, before the 
two orders of units have had their unlikenesses so far diminish- 
ed, that they will no longer do this. The same principles 
explain for us the variable results of imion between nearly- 
related organisms. According to the contrasts among the 
physiological units they inherit from parents and ancestors ; 
according to the unlike proportions of the contrasted units 
which they severally inherit ; and according to the degrees 
of segregation of such units in different sperm-ceUs and 
germ-cells ; it may happen that two kindred individuals will 
produce the ordinary number of offspring, or will produce 
none ; or will at one time be fertile and at another not ; or 
will at one time have offspring of tolerable strength, and at 
another time feeble offspring. 

To the like causes are also ascribable the phenomena of 
Variation. These are unobtrusive while the tolerably-uni- 
form conditions of a species maintain tolerable uniformity 
among the physiological units of its members ; but they 
become obtrusive when differences of conditions, entailing 


considerable functional differences, have entailed decided dif- 
ferences among the physiological units ; and when the differ- 
ent physiological units, differently mingled in every individual, 
come to be variously segregated and variously combined. 

Did space permit, it might be shown that this hypothesis 
is a key to many further facts — ^to the fact that mixed races 
are comparatively plastic under new conditions ; to the fact 
that pure races show predominant influences when crossed 
with mixed races ; to the fact that while mixed breeds are 
often of larger growth, pure breeds are the more hardy— 
have functions less-easily thrown out of balance. But with- 
out further argument, it will, I think, be admitted, that the 
power of this hypothesis to explain so many phenomena, and 
to bring under a common bond phenomena that seem so little 
allied, is strong evidence of its truth. And such evidence 
gains greatly in strength on observing that this hypothesis 
brings the facts of Genesis, Heredity, and Variation into har- 
mony with first principles. When we see that these plastic 
physiological units, which we find ourselves obliged to assume, 
are just such more integrated, more heterogeneous, more un- 
stable, and more multiform atoms, as would result from con- 
tinuance of the steps through which organic matter is reached — 
when we see that the differentiations of them assumed to oc- 
cur in differently- conditioned aggregates, and the equilibra- 
tions of them assumed to occur in aggregates which maintain 
constant conditions, are but corollaries from those universal 
principles implied by the persistence of force — when we see 
that the maintenance of life in the successive generations of a 
species, becomes a consequence of the continual incidence of 
new forces on the species, to replace the forces that are ever 
being rhythmically equilibrated in the propagation of the 
species — ^and when we thus see that these apparently-excep- 
tional phenomena displayed in the multiplication of organic 
beings, fall into their places as results of the general laws of 
Evolution; we have weighty reasons for entertaining the 
hypothesis which affords us this interpretation. 

19 • 




§ 98. That orderly arrangement of objects called Classic 
fication, has two purposes ; which, though not absolutely dis* 
tinct, are distinct in great part. It may be employed io 
facilitate identification ; or it may be employed to organize 
our knowledge. If a librarian places his books in the alpha- 
betical succession of the author's names, he places them in 
such way that any particular book may easily be found ; but 
not in ^uch way that books of a given nature stand together* 
When, conversely, he makes a distribution of books accord- 
ing to their subjects, he neglects various superficial similari- 
ties and distinctions, and groups them according to certain 
primary and secondary and tertiary attributes, which sever- 
ally imply many other attributes — groups them so that any 
one volume being inspected, the general characters of all the 
neighbouring volumes may be inferred. He puts together 
in one great division, all works on History ; in another all 
Biographical works ; in another all works that treat of 
Science ; in another Voyages and Travels ; and so on. Each 
of his great groups he separates into sub-groups ; as when 
be puts different kinds of pure Literature, under the heads 
of Fiction, Poetry, and the Drama. In some cases he 
makes sub-sub-groups ; as when, having divided his Scientific 
treatises into abstract and concrete, putting in the one Logic 
and Mathematics, and in the other Physios, Astronomy, Ge- 


ology, Chemistry, Physiology, &c. ; he goes on to sub-divide 
his books on Physics, into those which treat of Mechanical 
Motion, those which treat of Heat, those which treat of Light, 
of Electricity, of Magnetism. 

Between these two modes of classification, note the essen- 
tial distinctions. Arrangement according to any single con- 
spicuous attribute is comparatively easy, and is the first that 
suggests itself: a child may place books in the order of their 
sizes, or according to the styles of their bindings. But ar- 
rangement according to combinations of attributes, which, 
though fundamental, are not conspicuous, requires analysis ; 
and does not suggest itself till analysis has made some pro- 
gress. Even when aided by the information which the author 
gives on his title page, it requires considerable knowledge to 
classify rightly an essay on Polarization ; and in the absence 
of a title page, it requires much more knowledge. Again, 
classification by a single attribute, which the objects possess 
in different degrees, may be more or less serial, or linear. 
Books may be put in the order of their dates, in single file ; 
or if they are grouped as works in one volume, works in two 
volumes, works in three volumes, &c., the groups may be 
placed in an ascending succession. But groups severally 
formed of things distinguished by some common attribute 
which implies many other attributes, do not admit of serial 
arrangement. You cannot rationally say, either that His- 
torical Works should come before Scientific Works, or Scien- 
tific Works before Historical Works ; nor of the sub-divi- 
sions of creative Literature, into Fiction, Poetry, and the 
Drama, can you give a good reason why any one should take 
precedence of the others. 

Hence this grouping of the like and separation of the un- 
like, which constitutes Classification, can reach its complete 
form only by slow steps. We saw {First Principles, § 36) 
that, other things equal, the relations among phenomena are 
recognized in the order of their conspicuousness ; and that, 
other things equal, they are recognized in the order of their 


simplicity. The first classifications are sure, therefore^ to be 
groupings of objects that resemble each other in external or 
easily-perceived attributes, and attributes that are not of com- 
plex characters. Those likenesses among things which are 
due to their possession in common of simple obvious properties, 
may or may not coexist with further likenesses among them. 
When geometrical figures are classed as curvilinear *and 
rectilinear, or when the rectilinear are divided into trilateral, 
quadrilateral, &c., the distinctions made, connote various 
other distinctions, with which they are necessarily bound 
up ; but if liquids be classed according to their visible cha- 
racters — ^if water, alcohol, sulphuret of carbon, &c., be 
grouped as colourless and transparent, we have things placed 
together which are unlike in their essential natures. Thus, 
where the objects classed have numerous attributes, the pro- 
babilities are, that the early classifications, based on simple 
and manifest attributes, unite under the same head many 
objects that have no resemblances in the majority of their 
attributes. Aa the knowledge of objects increases, it be* 
comes possible to make groups of which the members have 
more numerous properties in common ; and to ascertain what 
property, or combination of properties, is most characteristiG 
of each group. And the classification eventually arrived at, 
is one in which the segregation has been carried so far, that 
the objects integrated in each group have more attributes in 
common with one another, than they have in common with 
any excluded objects ; one in which the groups of such groups 
are integrated on [the same principle ; and one in which the 
degrees of differentiation and integration are proportioned to 
the degrees of intrinsic unlikeness and likeness. And the 
ultimate classification, while it serves most completely to 
identify the things, serves also to express the greatest amount 
of knowledge concerning the things — enables us to predicate 
the greatest number of facts concerning each thing ; and by 
so doing proves that it expresses the most precise corre- 
spondence between our conceptions and the realities. 


§ 99. Biological classifications illustrate well these phases,, 
through which classifications in general necessarily pass. 
In early attempts to arrange organic beings in some sys- 
tematic manner, we see at first, a guidance by conspicuous 
and simple characters, and a tendency towards arrangement 
in linear order. In successively later attempts, we see 
more regard paid to combinations of characters which are 
essential but often inconspicuous; and a gradual abandon- 
ment of a linear aiTangement for an arrangement in di- 
vergent groups and re-divergent sub-groups. 

In the popular mind, plants are still classed under the 
heads of Trees, Shrubs, and Herbs ; and this serial classing 
according to the single attribute of magnitude, swayed the 
earliest observers. They would have thought it absurd to 
call a bamboo, thirty feet high, a kind of grass ; and would 
have been incredulous if told that the 'Hart's-tongue should 
be placed in the same great division with the Tree-ferns. 
The zoological classifications that were current before Na- 
tural History became a science, had divisions similarly super- 
ficial and simple. Beasts, Birds, Fishes, and Creeping-things, 
are names of groups marked off from one another by con- 
spicuous differences of appearance and. modes of life — crea- 
tures that walk and run, creatures that fly, creatures that live 
in the water, creatures that crawl. And these groups were 
thought of in the order of their importance. 

The first arrangements made by naturalists were based 
either on single characters, or on very simple combinations 
of characters. Describing plant-classifications, Lindley 
says : — " Rivinus invented, in 1690, a system depend- 
ing upon the formation of the corolla ; Kamel, in 1693, 
upon the fruit alone ; Magnol, in 1720, on the calyx and 
corolla ; and finally, Linnaeus, in 1731, on variations in the 
stamens and pistil." In this last system, which has been for 
so long current as a means of identification, simple external 
attributes are still depended on; and an arrangement, in 
great measure serial, is based on the degrees in which these 


attributes are possessed. In 1703, some thirty years before 
the time of Linnseus, our countryman Bay had sketched the 
outlines of a more advanced system. He said that — 

Plants are either 

Flowerless, or 

Flowering ; and these are 
Dicotyledones, or 
Among the minor groups which he placed under these 
general heads, "were Fungi, Mosses, Ferns, Composites, 
CichoracesB Umbellifers, Papilionaceous plants. Conifers, La- 
biates, &c., under other names, but with limits not very dif- 
ferent from those now assigned to them.*' Being much in 
advance of his age. Bay's ideas remained dormant until the 
time of Jussieu ; by whom they were developed into what 
has become known as the Natural System. Passing through 
various modifications in the hands of successive botanists, 
the Natural System has now taken the following form ; which 
I copy (adding the alliances to the classes) from Prof. 
Lindley's Vegetable Kingdom.^ 

* From this table I haye omitted the class Rhizogena^ which other botanists 
do not agree with Lindley in regarding as a separate class. The plants respect* 
ing which there has arisen this difference of opinion, are certain flowering 
plants, which grow parasitically on the roots of trees. The reasons assigned by 
Endlicher and Lindley, for erecting them into a separate group of Phaenogams, 
are, that in place of true leaves they have only cellular scales ; that the stem is 
an amorphous fungous mass, imperfectly supplied with spiral vessels ; and that 
they are without chlorophyll. Mr Griffith and Dr Hooker, however, have given 
preponderating reasons why they should be restored to the class Exogens. It 
seems here worth remarking, that certain zoological fieuits suggest an explanation 
of these anomalous botanical facts ; and confirm the conclusion reached by Dr 
Hooker and Mr Griffith. It very commonly happens that animal-parasites are 
aberrant forms of the types to which they belong ; and, by analogy, we may not 
unreasonably expect to find among .parasitic plants, the most aberrant forms of 
vegetal types. More than this is]true. The kind of aberration which we see in the 
one case, we see in the other ; and in both cases, the meaning of the aberration is 
manifest. In such J^nzoa as the Zernea, the Crustacean type is disguised by the 
almost entire loss of the limbs and organs of sense, by the simplification of the 
digestive apparatus, and by the great development of the reproductive system : 



Stems and leaves undistingoishable 
Stems and leaves distinguishable 

Asexual, or Flowerleu Plants. 

I. Thallooehs < Fuugales 


< LycotK)dalc8 

Sexual, or Flowering Plants, 

Wood of stem youngest in centre ; 
cotyledon single. 

Loaves parallel-veined, permanent ; 
wood confused IIL EmDoobhs ' 

Leaves net-voined, deciduous ; 
wood, when perennial, arraniiced 
in a ciroIe.with a central pith lY. Diottooxkb. 

Wood of stem youngest at circum- 
ference, always concentric ; coty- 
ledons two or more. 

Seeds quite naked V. GrMvoi^Eirs. 












Seeds enclosed in socd'vesseU VL EIooens 





rAmen talcs 
I Urticalea 
I Buphorbiales 
^ Ac. &o. 
J Cistolea 
] Mai vales 
^ Ac. Ac. 
J Daphnales 
^^ Ac. Ac. 
I Cactales 
^ AcAor 

Here, linear arrangemdnt has disappeared : there is a 
breaking up into groups and sub-groups and sub-*sub-groupS| 
which do not admit of being placed in serial order, but only 
in divergent and re-divergent order. Were there space to 
exhibit the way in which the Alliances are subdivided into 
Orders, and these into Genera) and these into Species ; the 

the parts no longer needed, abort, and those parts develop which favour the 
preservation of the race. Similarly in the Mhizogens, the abortive development 
of the leaves, the abafiDce of chlorophyll, and the imperfect supply of spiral 
vessels, are changes towards a structure fit for a plant which lives on the juices 
absorbed from another plant; while the rapid and great development of the 
fructifying organs, are correlative changes advantageous to a plant, the seeds of 
which have but small chances of rooting themselves. And just the same reason 
that exists for the production of immensely numerous but extremely small eggs 
by £ntozoaf exists for the production by RMzogms^ of seeds that are great in 
number and almost sporo-like in size. 


same principlo of co-ordination wotdd be still further mani- 
fested. On studying the definitions of these primary^ se- 
condary, and tertiary classes, it will be found that the 
largest are marked off from each other by some attribute 
which connotes sundry other attributes ; that each of the 
smaller classes comprehended in one of these largest classes, 
is marked off in a similar way from the smaller classes 
bound up with it; and that so, each successiyely smaller 
class, has an increased number of co*existing attributes. 

§ 100. Zoological classification has had a parallel history. 
The first attempt which we need notice, to arrange animals 
in such a way as to display their affinities, is that of Lin- 
naeus. He grouped them thus :* — 

Gl. 1« Mammalia. Ord, Primates, Bruta, Fere, Glires, Fecora, Bellus, 

Gl. 2. Ayeb. Ord, Accipitres, Ficie, Anseres, Gralloe, Gallinft, Passerea. 

Gl. 3. Amphibia. Ord, Reptiles, Serpentes, Nantes. 

Gl. 4. FiscES. Ord, Apodes, Jugulares, Thoracici, Abdominales. 

Gl. 5. Insecta. Ord, Coleoptera, Hemiptera, Lepidoptera, Neuroptera, 
Diptera, Aptera. 

Gl. 6. YxRMss. Ord, Intestina, Mollasca, Testacea, Lithophyta, Zoo- 

This arrangement of classes, is obviously based on ap- 
parent gradations of rank ; and the placing of the orders 
similarly betrays an endeavour to make successions, begin'- 
ning with the most superior forms and ending with the 
most inferior forms. While the general and vague idea 
of perfection, determines the leading character of the 
classification, its detailed groupings are determined by 
the most conspicuous external attributes. Not only Lin- 
nsus, but his opponents, who proposed other systems, were 
"under the impression that animals were to be arranged 
together into classes, orders, genera, and species, according to 
their more or less close external resemblance.^' This con- 
ception survived till the time of Ouvier. "Naturalists," 

* This classification, and the three which follow it, I quote (abridging some 
of them) from Prof. Agassiz's ** Essay on Classification.'* 


says Agassiz^ ''were bent upon establishing one continual 
uniform series to embrace all animals, between the links of 
which it was supposed there were no imequal intervals. 
The watchword of their school was: Natura non facii 
saUum. They called their system la chaine des itreaJ^ 

The classification of Cuvier, based on internal organization 
instead of external appearance, was a great advance. He 
asserted that there are four principal forms, or four general 
plans, on which animals are constructed ; and in pursuance 
of this assertion, he drew out the following scheme. 

First Branch, Animalia Vertebrata. 
Cl. 1. Mammalia. 
Cl, 2. Birds. 
Cl. 3. Rbptilia. 
Cl. 4. Fishes. 

Second Branch. Animalia Mollusca. 
Cl. I. Cephalapoda. 
Cl. 2. Pteropoda. 
Cl. 8. Gasteropoda. 


Cl, 6. Brachiopoda. 
Cl. 6. Cirrhopoda, 

Third Branch. Animalia Articulata. 
Cl. 1. Annrlides. 
Cl. 2. Crustacea. 
Cl. 3. Arachnides. 
Cl. 4. Insecis. 

Fourth Branch. Animalia Radiata. 
Cl. 1. Echinoderms. 
Cl. 2. Intestinal Worms. 


Cl. 4. Polypi. 
Cl. 5. Infusoria. 



But though Cuvier emancipated himself from the cdncep- 
tion of a serial progression throughout the Animal- King- 
dom ; sundry of his contemporaries and successors remained 
fettered by the old error. Less regardftil of the differently* 
co-ordinated sets of attributes displayed by the different sub- 
kingdoms ; and swayed by the belief in a progressive develop- 
ment, which was erroneously supposed to imply the possibility 
of arranging animals in a linear series ; they persisted in 
thrusting organic forms into a quite unnatural order. The 
following classification of Lamarck illustrates this. 



Apathetic Anikals. 


1. Infusoria. 


2. Polypi. 


3. Radla.rl\. 




6. Vermes. 

Sensitive Animals. 


6. Insects. 


7. Arachnids. 


8. Crustacea. 


9. Annelids. 







III. Intelligent Animals. 

Cl. 13. 
Cl. 14. 
Cl. 15. 
Cl. 16. 


Do not feelj and move only by 
their excited irritability. No brain, 
not elongated medullary mass; no 
senses ; forms varied ; rarely articu- 

Feel| but obtain from their sensa- 
tions only perceptions of object.s, a 
sort of simple ideas, which they are 
unable to combine to obtain complex 
> ones. No vertebral column ; a brain 
and mostly an elongated medullary 
mass; some distinct senses; muscles 
attached under the skin ; form sym- 
metrical, the parts being in pairs. 


Eeel; acquire preservable ideas; 
perform with them operations by 
which they obtain others ; are intel- 
b'gent in different degrees. A ver- 
> tebral column ; a brain and a spinal 
marrow; distinct senses; the mus- 
cles attached to the internal skele- 
ton; form symmetrical, the parts 
being in pairs. 


Passing over sundry classifications in which the serial 
arrangement dictated by the notion of ascending complexity^ 
is variously modified by the recognition of conspicuous 
anatomical facts, we come to the classifications which recognize 
another order of facts— those of development. The embryo- 
logical inquiries of Von Baer, led him to arrange animals aS 
follows : — 

I. Peripheric Type. (Radiata.) Evolutio radiata. The 
development proceeds from a centre, producing 
identical parts in a radiating order. 
II. Massive Type. (Mollusca.) Evolutio coniorta. The 
development produces identical parts curved around 
a conical or other space. 

III. Longitudinal Type. (Articulata.) Evolutio gemina. 

The development produces identical parts arising on 
both sides of an axis, and closing up along a line 
opposite the axis. 

IV. Doubly Symmetrical type. (Vertebrata.) Etolutio 

bigemina. The development produces identical 
parts arising on both sides of an axis, growing up- 
wards and downwards, and shutting up along two 
lines, so that the inner layer of the germ is inclosed 
below, and the upper layer above: The embryos of 
these animals have a dorsal cord, dorsal plates, and 
ventral plates, a nervous tube and branchial fissures. 

Recognizing these fundamental difPerences in the modes of 
evolution, as answering to fundamental divisions in the 
animal kingdom, Von Baer shows (among the Vertebrata at 
least) how the minor differences that arise at successively 
later stages of evolution, correspond with the minor divisions. 

Like the modern classification of plants, the classification 
of animals that has now been arrived at, is one in which the 
linear order is completely broken up. In his lectures at the 
Royal Institution, in 1857, Prof. Huxley expressed the rela- 



tions existing among the several great groups of the animal 
kingdom, by placing these groups at the ends of four or five 
radii, diverging from a centre. The diagram I cannot 
obtain ; but in the published reports of his lectures at the 
School of Mines the groups were arranged thus :— 









Cephalopoda Heteropoda 

{Pulmonata Gasteropoda- 
Fteropoda monoecia 




Insecta Arachnida 

Myriapoda Crustacea 

Annellata Scoleidse 



Ilydrozoa Actinozoa. 





What remnant there may seem to be of linear succession 
in some of these sub-groups, is merely an accident of typo- 
graphical convenience. Each of them is to be regarded 
simply as a cluster. Were Prof. Huxley now to revise this 
scheme, he would probably separate more completely some of 
the great sub-groups, in conformity with the views expressed 
in his Hunterian Lectures delivered at the College of Sur- 
geons in 1863. And if he were further to develop the 
arrangement, by dispersing the sub-groups and sub-sub- 
groups on the same principle, there would result an arrange- 




ment perhaps not very much unlike that shown in the 
annexed diagram. 

• W3famma/ut 



AmfikiSia \ Fiscea 
\ • 


* tf ^Qatterofioda. 

* • dioelet- 
Gnsterefi-odu, •Putmcna^a 
fnenirc$a> • • 


• • ^"^"""^^^^ 


Mollusc oXda 

JLaeUMita * • ' V •I^lyx on / 



* »*^*Craataeea 



A N N l/ LO S.A 
S^ecUeidcL • ^ 
'• ••• 


/ / * 

JEt^Unedtr^natu %*, * 
. » / •• 

. // 

• ^O^ngarinida 
JBtAUofi.cdi(\^ ^ 


• - / SAcngida Infusoria 

ffydrcaca. , 


In this diagram, the dots represent orders, the names of 
which it is impracticahle to insert. If it be supposed that 
when magnified, each of these dots resolves itself into a 
cluster of clusters, representing genera and species, an ap- 
proximate idea will be formed of the relations among the 
successively-subordinate groups constituting the animal king- 


dom. Besides the subordination of groups and their general 
distribution, some other facts are indicated. By the distances 
of the great divisions from the general centre, are rudely 
symbolized their respective degrees of divergence from the 
form of simple, undifferentiated organic matter ; which we 
may regard as their common source. Within each group, 
the remoteness from the local centre represents, in a rough 
way, the degree of departure from the general plan of the 
group. And the distribution of the sub-groups within each 
group, is in most cases such, that those which come nearest 
to neighbouring groups, are those which show the nearest 
resemblances to them—in their analogies though not in their 
homologies. No diagram, however, can give a correct con- 
ception. Even supposing the above diagram expressed the 
relations of animals to one another as truly as they can be 
expressed on a plane surface, (which of course it does not,) it 
would still be inadequate. Such relations cannot be repre- 
sented in space of two dimensions; but only in space of three 

§ 101. While the classifications of botanists and zoologists 
have become more and more natural in their arrangements, 
there has grown up a certain artificiality in their abstract 
nomenclature. When aggregating the smallest groups into 
larger groups, and these into groups still larger, natur- 
alists adopted certain general terms expressive of the suc- 
cessively more comprehensive divisions; and the habitual 
use of these terms, needful for purposes of convenience, has 
led to the tacit assumption that they answer to actualities in 
Nature. It has been taken for granted that species, genera, 
orders, and classes, are assemblages of definite values — that 
every genus is the equivalent of every other genus, in respect 
of its degree of distinctness ; and that orders are separated 
by Hnes of demarcation that are as broad in one place as 
another. Though this conviction is not a formulated one, 
yet the disputes continually arising among naturalists on the 


questions, whether such and such organisms are specifically 
or generically distinct, and whether this or that peculiarity 
is or is not of ordinal importance, imply that the conviction 
is entertained even where . it is not avowed. Yet that dif- 
ferences of opinion Uke these continually arise, and remain 
unsettled, except when they end in the establishment of sub- 
species, sub-genera, sub-orders, and sub-classes, sufficiently 
shows that no such conviction is justifiable. And this is 
equally shown by the impossibility of obtaining any definition 
of the degree of difference, which warrants each further eleva- 
tion in the hierarchy of classes. 

It is, indeed, a wholly gratuitous assumption that organ- 
isms admit of being placed in groups of equivalent values ; 
and that these may be united into larger groups that are 
also of equivalent values ; and so on. There is no a priori 
reason for expecting this ; and there is no a posteriori evi- 
dence implying it, save that which begs the question — that 
which asserts one distinction to be generic and another to be 
ordinal, because it is assumed that such distinctions must be 
either generic or ordinal. The endeavour to thrust plants 
and animals into these definite partitions, is of the same 
nature as the endeavour to thrust them into a linear series. 
Not that it does violence to the facts in anything like the 
same degree ; but still, it does violence to the facts. Doubt- 
less the making of divisions and sub-divisions, is extremely 
useful ; or rather, it is absolutely necessary. Doubtless, too, 
in reducing the facts to something like order, they must be 
partially distorted. So long as the distorted form is not 
mistaken for the actual form, no harm results. But it is 
needful for us to remember, that while our successively 
subordinate groups have a certain general correspondence 
with the realities, they inevitably give to the realities a 
regularity which does not exist. 

§ 102. A general truth of much significance is exhibited 
in these classifications. On observing the natures of the 



attributes which are common to the members of any group 
of the first, second, third, or fourth rank, we see that groups 
of the widest generality are based on characteristics of the 
greatest importance, physiologically considered ; and that the 
characteristics of the successively-subordinate groups, are 
characteristics of successively-subordinate importance. The 
structural peculiarity in which all members of one sub- 
kingdom differ from aU members of another sub-kingdom, is 
a peculiarity that affects the vital actions more profoundly, 
than does the structural peculiarity which distinguishes all 
members of one class from all members of another class. 
Let us look at a few cases. 

We saw (§ 66), that the broadest division among the 
functions is the division into "the accumulation of force 
(latent in food) ; the expenditure of force (latent in the 
tissues and certain matters absorbed by them); and the 
transfer offeree (latent in the prepared nutriment or blood) 
from the parts which accumtdate to the parts which expend." 
Now the lowest animals, united under the general name 
Protozoa, are those in which there is either no separation of 
the parts performing these functions or very indistinct separ- 
ation : in the JRhizopoda, all parts are alike accumulators of 
force, expenders of force, and transferrers of force; and 
though in the most differentiated members of the group, the 
Infusoria, there are something like specializations corre- 
sponding to these functions, yet there are no distinct tissues 
appropriated to them. The animals known as Ccelenterata 
are characterized in common by the possession of a part 
which accumulates force more or less marked off from the 
part which does not accumulate force, but only expends it ; 
and the Hydrozoa and Actinozoa, which are sub-divisions of 
the Ccelenterata, are contrasted in this, that in the one these 
parts are very indefinitely distinguished, but in the other 
definitely separated, as well as more complicated. Besides a 
completer differentiation of the organs respectively devoted 
to the accumulation of force and the expenditure of force. 


the animals classed as Mollmcoida, possess rude appliances 
for the transfer of force: the peri- visceral sac, or closed 
cavity between the intestine and the waUs of the body, 
serves as a reservoir of absorbed nutriment, from which the 
surrounding tissues take up the materials they need. The 
more highly-organized animals, belonging to whichever sub- 
kingdom, all of them possess definitely-constructed channels 
for the transfer of force ; and in all of them, the function of 
expenditure is divided between a directive apparatus and 
an executive apparatus — a nervous system and a muscular 
system. But these higher sub-kingdoms are clearly separated 
from each other by differences in the relative positions of 
their component sets of organs. Prof. Huxley defines the 
type of the Vertebrata, as one in which the ganglionic nervous 
system lies on the dorsal side of the alimentary canal, while 
the central vascular system lies on ite ventral side ; and one 
which is yet further characterized by the possession of a 
second, and more conspicuous, nervous system, placed on the 
dorsal side of the vertebral axis — ^an extra endowment which 
is perhaps the most essentially distinctive. The types of the 
Annulosa and Moilusca, are together marked off from the 
vertebrate type, by the singleness of the nervous system, and 
by its occupation of the ventral side of the body: the 
habitual attitudes of annulose and molluscous creatures, is 
such that the neural centres are below the alimentary canal 
and the haamal centres above. And while by these traits the 
annulose and molluscous types are separated from the verte- 
brate, they are separated from each other by this, that in 
the one the body is ''composed of successive segments, 
usually provided with limbs,*' but the other, the body is not 
segmented, '' and no true articulated limbs are ever de- 

The sub-kingdoms being thus distinguished from one an- 
other, by the presence or absence of parts devoted to funda- 
mental functions, or else by differences in the distributions of 
such parts ; we find, on descending to the classes, that these 

20 • 


are distinguished from each other^ either by modifications in 
the structures of fundamental parts, or by the presence or 
absence of subsidiary parts, or by both. Fishes and Am- 
phibia are imlike higher Tcrtebrates in possessing branchisD ; 
either throughout life or early in life. And every higher 
vertebrate, besides having lungs, is characterized by having, 
during development, an amnion and an allantois. Mammals, 
again, are marked off from Birds and Reptiles by the 
presence of mammae, as well as by the form of the occipital 
condyles. Among Mammals, the next division is based on 
the presence or absence of a placenta. And divisions of the 
Placentalia are mainly determined by the characters of the 
organs of external action. 

Thus, without multiplying illustrations and without de- 
scending to genera and species, we see that, speaking gener- 
ally, the successively smaller groups, are distinguished from 
one another by traits of successively less importance, physio- 
logically considered. The attributes possessed in common 
by the largest assemblages of organisms, are few in number 
but all-essential in kind — affect fundamentally the most vital 
actions. Each secondary assemblage, included in one of the 
primary assemblages, is characterized by further common 
attributes that influence the functions less profoundly. And 
so on with each lower grade of assemblage. 

§ 103. What interpretation is to be put on these truths of 
classification P We find that organic forms admit of an 
arrangement everywhere expressive of the fact, that along 
with certain attributes, certain other attributes, which are 
not directly connected with them, always exist. How are 
we to account for this fact P And how are we to account for 
the fact that the attributes possessed in common by the 
largest assemblages of forms, are the most vitally-important 
attributes P 

No one can believe that combinations of this kind may 
have arisen fortuitously. Or if any one believes this, it is 


easy to prove to him that the law of probabiKties negatives 
the assumption. Even supposing fortuitous combinations of 
attributes might result in organisms that would work, we 
should still be without a clue to this special mode of com- 
bination. The chances would be iniGlnity to one against 
organisms which possessed in common certain fundamental 
attributes, having also in common numerous non-essential 

No one, again, can allege that such combinations are 
necessary, in the sense that all other combinations are im- 
practicable. There is not, in the nature of things, any 
reason why creatures covered with feathers should always 
have beaks : jaws holding teeth would, in many cases> 
have served them equally well or better. The most general 
characteristic of an entire sub-kingdom, equal in extent 
to the Vertebrata, might have been the possession of nicti- 
tating membranes ; while the internal organizations through- 
out this sub-kingdom, might have been on many different 

If, on the other hand, this peculiar subordination of attri- 
butes which organic forms display, be ascribed to design, other 
difficulties suggest themselves. To suppose that a certain 
plan of organization was fixed on by a Creator, for each vast 
and varied group, the members of which were to lead many 
different modes of life ; and that he bound himself to adhere 
rigidly to this plan, even in the most aberrant forms of the 
group, where some other plan would have been more appro- 
priate ; is to ascribe a very strange motive. When we dis- 
cover that the possession of seven cervical vertebrae is a 
general characteristic of mammals, whether the neck be im- 
mensely long, as in the giraffe, or quite rudimentary, as in 
the whale ; shall we say that though, for the whale's neck, 
one vertebra would have been equally good, and though, for 
the giraffe's neck, a dozen would probably have been better 
than seven, yet seven was the number adhered to in both 
cases, because seven was fixed upon for the mammalian type P 


And then, when it tums out that this possession of seven 
cervical vertebrae is not an absolutely-universal characteristic 
of mammals, shall we conclude that while, in a host of cases, 
there is a needless adherence to a plan for the sake of 
consistency, there is yet, in some cases, an inconsistent 
abandonment of the plan P I think we may properly refuse 
to draw any such conclusion. 

What, then, is the meaning of these peculiar relations of 
organic forms ? The answer to this question must be post- 
poned. Having here contemplated the problem as presented 
in these wide inductions which naturalists have reached ; and 
having seen what proposed solutions of it are inadmissible ; 
we shall see, in the next division of this work, what is the 
only possible solution. 



§ 104. There is a distribution of organisms in Space, and 
there is a distribution of organisms in Time. Looking first 
at their distribution in Space, we observe in it two different 
classes of facts. On the one hand, the plants and animals of 
each species, manifestly have their habitats limited by ex- 
ternal conditions : they are necessarily restricted to spaces 
in which their vital actions can be performed. On the other 
hand, the existence of certain conditions does not determine 
the presence of organisms that are the fittest for them : there 
are many spaces perfectly adapted for life of a high order, 
in which only life of a much lower order is found. "While, 
in this inevitable restriction of organisms to environments 
with which their natures correspond, we find a negative 
cause of distribution ; there remains to be found that positive 
cause -of distribution, whence results the presence of organ- 
isms in some of the places appropriate to them, and their 
absence from other places that are equally appropriate and 
more appropriate. Let us consider the phenomena under 
these categories. 

§ 105. Facts which illustrate the limiting influence of sur- 
rounding conditions, are abundant, and familiar to all read- 
ers. It will be needful, however, here to cite a few typical 
ones of each order. 


The oonfinement of di£Eerent kinds of plants and different 
kinds of animals, to the media for which they are severally 
adapted, is the broadest fact of distribution. We have ex- 
tensive groups of plants that are respectively sub-aerial and 
sub-aqueous ; and of the sub-aqueous, some are exclusively 
marine, while others exist only in rivers and lakes. Among 
animals, we similarly find some classes confined to the air 
and others to the water ; and of the water-breathers, some 
are restricted to salt water and others to fresh water. Less 
familiar is the fact, that within each of these strongly con- 
trasted media, there are further wide-spread limitations. In 
the sea, certain organisms exist only between certain depths, 
while other organisms exist only between other depths — ^the 
limpet within the littoral zone, and the Ohbigerina at the 
bottom of the Atlantic ; and on the land, there are Floras 
and Faunas peculiar to low regions, and others peculiar to 
high regions. Next we have the well-known geographical 
limitations, made by climate. There are temperatures that 
restrict each kind of organism between certain isothermal 
lines ; and hygrometric states that prevent the spread of 
each kind of organism beyond areas having a certain hu- 
midity or a certain dryness. Besides such general limita- 
tions, we find much more special limitations. Some minute 
vegetal forms occur only in snow. Hot springs have their 
pecidiar Inftzsoria, The habitats of certain Fungi are mines 
or other dark places. And there are creatures unknown be- 
yond the water contained in particular caves. After 
these limits to distribution imposed by physical conditions, 
come limits of a different class, imposed by the presence 
or absence of other organisms. Obviously, graminivorous 
animals are confined within tracts which produce plants fit 
for them to feed on. Large carnivores cannot exist out of 
regions where there are creatures numerous enough and 
large enough to serve for prey. The requitements of the 
sloth, limit it to certain forest-covered spaces ; and there can 
be no insectivorous bats, where there are no night-flying 


insects. To these dependences of the relatively-superior 
organisms on the relatively-inferior organisms which they 
consume^ must be added certain reciprocal dependences of 
the inferior on the superior. Mr Darwin's inquiries have 
shown how generally the fertilization of plants is due to the 
agency of insects ; and how certain plants, being fertilizable 
only by insects of a certain structure, are limited to regions 
inhabited by insects of this structure. Conversely, the spread 
of organisms is often bounded by the presence of particular 
organisms beyond the bounds — either competing organisms 
or organisms directly inimical. A plant that is fit for some 
territory adjacent to its own, fails to overrun it, because the 
territory is pre-occupied by some plant that is its superior, 
either in fertility or power of resisting destructive agencies ; 
or else because there lives in the territory some mammal 
which browses on its foliage, or bird which devours nearly all 
its seeds. Similarly, an area in which animals of a particu- 
lar species might thrive, is not colonized by them, because 
they are not fleet enough to escape some beast of prey inhab- 
iting this area ; or because the area is infested by some in- 
sect which destroys them, as the tsetse destroys the cattle in 
parts of Africa. Yet another more special series of 

limitations, accompanies parasitism. There are parasitic 
plants that flourish only on trees of some few kinds ; and 
others that have certain animals for their habitats — as the 
fungus which is fatal to the silk-worm, or that which so 
strangely grows out of a New Ziealand caterpillar. Of 
animal-parasitism we have various kinds : severally involv- 
ing their specialities of distribution. We have that kind in 
which one creature uses another for purposes of locomotion ; 
as the ChelonoUa uses the turtle, and as a certain Ac- 
tinia uses the shell inhabited by a hermit-crab. We have 
that kind in which one creature habitually accompanies 
another to share its prey ; like the annelid which takes up 
its abode in the shell occupied by a hermit-crab, and snatches 
from the hermit-crab, the morsels of food it is eating. We 


have again the commoner parasitism of the Epizoa — animals 
which attach themselves to the surfaces of other animals, and 
feed on their juices or on their secretions. And once more, we 
have the equally common parasitism of the Entozoa — creatures 
which live within other creatures. Besides being restricted 
in its distribution to the bodies of the organisms it infests, 
each species of parasite has usually still narrower limitations : 
in some cases the infested organisms furnish fit habitats for 
the parasites only in certain regions ; and in other cases, only 
when in certain constitutional states. There are 

various more indirect modes in which the distributions of 
organisms affect each other. Plants of particular kinds are 
eaten by animals, only in the absence of kinds that are 
preferred to them ; and the prosperity of such plants, hence 
partly depends on the presence of the preferred plants. Mr 
Bates has pointed out that some South American butterflies, 
thrive in regions where insectivorous birds woidd else destroy 
them, because they closely resemble butterflies of another 
genus which are disliked by those birds. And Mr Darwin 
gives cases of dependence still more remote and involved. 

Such are the chief negative causes of distribution — ^the 
inorganic and organic agencies, that set bounds to the spaces 
which organisms of each species inhabit. Fully to under- 
stand their actions, we must contemplate them as working 
not separately, but in concert. "We have to regard the 
physical influences, varying from year to year, as now 
producing an extension or restriction of the habitat in this 
direction, and now in that; and as producing secondary 
extensions and restrictions, by their effects on other kinds of 
organisms. We have to regard the distribution of each 
organism, not only as affected by causes which favour multi- 
plication of prey or of enemies within its own area ; but also 
b}' causes which produce such results in neighbouring areas. 
We have to conceive the forces by which the limit is 
maintained, as including all metcorologic influences, united 


with the influences, direct or more or less remote, of nearly- 
all co-existing organisms. 

One general truth, indicated by sundry of the above illus- 
trations, calls for special notice — the truth that organisms 
are ever intruding on each other's spheres of existence. Of 
the various modes in which this is shown, the commonest is 
the invasion of territory. That tendency which we see in 
the human races, to overrun and occupy each other's lands, 
as well as the lands inhabited by inferior creatures, is a 
tendency exhibited by all classes of organisms in all va- 
rieties of ways. Among them, as among mankind, there are 
permanent conquests, temporary occupations, and occasional 
raids. Annual migrations are instances of this process in 
its most familiar form. Every spring an inroad is made into 
the area which our own fly-catchers occupy, by the swallows 
of the South ; and every winter the fieldfares of the North, 
come to share the hips and haws of our hedges with native 
birds — a partial possession of their territory, which entails 
on our native birds, some mortality. Besides these regularly- 
recurring raids, there are irregular ones : as of locusts into 
countries not usually visited by them ; or of strange birds 
which in small flocks from time to time visit areas adjacent 
to their own. Every now and then, an incursion ends in 
permanent settlement — perhaps in conquest over indigenous 
species. Within these few years, an American water-weed 
has taken possession of our ponds and rivers, and to some 
extent supplanted native water- weeds. Of animals, may be 
named a small kind of red ant, having habits allied to those 
of tropical ants, which has of late overrun many houses in 
London. The case of the rat, which must have taken to 
infesting ships within these few centuries, is a good illustra- 
tion of the readiness of animals to occupy new places that 
are available. And the way in which vessels visiting India, 
are cleared of the European cockroach by the kindred BMta 
orientalis, shows us how these successful invasions last only 
until there come more powerful invaders. Organ- 


isms encroach on one another's spheres of existence, in fur- 
ther ways than by trespassing on one another's areas : they 
adopt one another's modes of life. There are cases in which 
this usurpation of habits is slight and temporary ; and there 
are cases where it is marked and permanent. Orey crows 
frequently join gulls and curlews in picking up food between 
tide-marks ; and gulls and curlews may be occasionally seen 
many miles inland, feeding in ploughed fields and on moors. 
Mr Darwin has watched a fly-catcher catching fish. He 
says that the greater titmouse sometimes adopts the practices 
of the shrike, and sometimes of the nuthatch ; and that some 
South American woodpeckers are frugivorous, while others 
chase insects on the wing. Of habitual intrusions on the 
occupations of other creatures, one case is furnished by the 
sea-eagle ; which, besides hunting the surface of the land for 
prey, like the rest of the hawk-tribe, often swoops down upon 
fish. And Mr Darwin names a species of petrel that has 
taken to diving, and has a considerable, modified organiza- 
tion. These last cases introduce us to a still more 
remarkable class of facts of kindred meaning. This intrusion 
of organisms on one another's modes of life, goes to the ex- 
tent of intruding on one another's media. The great mass 
of flowering plants are terrestrial ; and are required to be so 
by their process of fructification. But there are some which 
live in the water, and protrude only their flowers above the 
surface. Nay, there is a still more striking instance : on the 
sea-shore may be found an alga a hundred yards inland, 
and a phaenogam rooted in salt-water. Among animals, 
these interchanges of media are numerous. Nearly all 
coleopterous insects are terrestrial ; but the water-beetle, 
which like the rest of its order is an air-breather, has 
aquatic habits. Water appears to be an especially unfit 
medium for a fly; and yet Mr Lubbock has lately dis- 
covered more than one species of fly living beneath the sur- 
face of the water, and coming up only occasionally for air. 
Birds, as a class, are especially fitted for an aerial existence ; 



but certain tribes of them have taken to an aquatic existence 
— swimming on the surface of the water and making continual 
incursions beneath its surface ; and there are some genera 
that have wholly lost the power of flight. Among mam- 
mals, too, which have limbs and lungs implying an organiza- 
tion for terrestrial life, may be named kinds that live more 
or less in the water, and are more or less adapted to it. We 
have water-rats and otters, which imite the two kinds of life, 
and show but little modification ; hippopotami passing the 
greater part of their time in the water, and somewhat more 
fitted to it ; seals living almost exclusively in the sea, and 
having the mammalian form greatly obscured ; whales 
wholly confined to the sea, and having so little the aspect of 
mammals as to be mistaken for fish. Conversely, sundry 
inhabitants of the water make more or less prolonged ex- 
cursions on the land. Eels migrate at night from one pool 
to another. There are fish with specially-modified gills, and 
fin-rays serving as stilts, which, when the rivers they in- 
habit are partially dried-up, travel in search of better quarters. 
And while some kinds of crabs do not make land-excursions 
beyond high-water mark, other kinds pursue lives almost 
wholly terrestrial. 

Joining together these two classes of facts, we must regard 
the bounds to each species' sphere of existence, as determined 
by the balancing of two antagonist sets of forces. The tend- 
ency which every species has to intrude on other areas, 
other modes of life, and other media, is restrained by the 
direct and indirect resistance of conditions, organic and inor- 
ganic. And these expansive and repressive energies, vary- 
ing continually in their respective intensities, rhythmically 
equilibrate each other — maintain a limit that perpetually 
oscillates from side to side of a certain mean. 

§ 106. As implied at the outset, the character of a region, 
when unfavourable to any species, sufficiently accounts for the 
absence of this species ; and thus its absence is not incon- 


gruous with the hypothesis, that each species was originally 
placed in the regions most favourable to it. But the absence 
of a species from regions that are favourable to it, cannot be 
thus accounted for. Were plants and animals localized wholly 
with reference to the fitness of their constitutions to surround- 
ing conditions, we might expect Floras to be similar and 
Faunas to be similar, where the conditions are similar ; and 
we might expect dissimilarities among Floras and among 
Faunas, proportionate to the dissimilarities of their conditions. 
But we do not find such anticipations verified. 

Mr Darwin says that " in the Southern hemisphere, if we 
compare large tracts of land in Australia, South Africa, and 
western South America, between latitudes 25° and 35°, we shall 
find parts extremely similar in all their conditions, yet it 
would not be possible to point out three faunas and floras 
more utterly dissimilar. Or again we may compare the pro- 
ductions of South America south of lat. 35° with those north 
of 25°, which consequently inhabit a considerably different cli- 
mate, and they will be found incomparably more closely related 
to each other, than they are to the productions of Australia 
or Africa under nearly the same climate.^' Still more striking 
are the contrasts which Mr Darwin points out, between closely- 
adjacent areas that are totally cut-off from each other. " No 
two marine faunas are more distinct, with hardly a fish, shell, 
or cr^,b in common, than those of the eastern and western 
shores of South and Central America ; yet these great faunas 
are separated only by the narrow, but impassable, isthmus of 
Panama." On opposite sides of high mountain-chains, also, 
there are marked differences in the organic forms — differ- 
ences not so marked as where the barriers are absolutely im- 
passable ; but much more marked than are necessitated by 
unlikenesses of physical conditions. 

Not less suggestive is the converse fact, that wide geogra- 
phical areas which offer decided geologic and meteorologic 
contrasts, are peopled by nearly-allied groups of organisms, if 
there are no barriers to migration. " The naturalist in tra- 


veiling, for instance, from north to south never fails to be 
struck by the manner in which successive groups of beings, 
specifically distinct, yet clearly related, replace each other. 
He hears from closely allied, yet distinct kinds of birds, 
notes nearly similar, and sees their nests similarly constructed, 
but not quite alike, with eggs coloured in nearly the same 
manner. The plains near the Straits of Magellan are inhabit- 
ed by one species of Bhea (American Ostrich), and north-ward 
the plains of La Plata by another species of the same genus ; 
and not by a true ostrich or emeu, like those found in Africa 
and Australia under the same latitude. On these same plains 
of La Plata, we see the agouti and bizcacha, animals having 
nearly the same habits as our hares and rabbits and belonging 
to the same order of Rodents, but they plainly display an 
American type of structure. We ascend the lofty peaks of 
the Cordillera and we find an alpine species of bizcacha ; we 
look to the waters, and we do not find the beaver or musk- 
rat, but the coypu and capybara, rodents of the American 
type. Innumerable other instances could be given. If we 
look to the islands off the American shore, however much 
they may differ in geological structure, the inhabitants, though 
they may be all peculiar species, are essentially American." 

What is the generalization that expresses these two groups 
of facts ? On the one hand, we have similarly-conditioned, 
and sometimes nearly-adjacent, areas, occupied by quite dif- 
ferent Faunas. On the other hand, we have areas remote from 
each other in latitude, and contrasted in soil as well as climate, 
which are occupied by closely-allied Faunas. Clearly then, as 
like organisms are not universally, or even generally, found 
in like habitats ; nor very unlike organisms, in very unlike 
habitats ; there is no manifest pre-determined adaptation of 
the organisms to the habitats. The organisms do not occur 
in such and such places, solely because they are either spe- 
cially fit for these places, or more fit for them than all other 

The induction under which these facts come, and which 


unites them with various other facts^ is a totally-different one. 
When we see that the similar areas peopled by dissimilar 
forms, are those between which there are impassable barriers ; 
while the dissimilar areas peopled by similar forms, are those 
between which there are no such barriers ; we are at once re- 
minded of the general truth exemplified in the last section : — 
the truth that each species of organism, tends ever to expand 
its sphere of existence — to intrude on other areas, other 
modes of life, other media ; and through these perpetuaUy- 
recurring attempts to thrust itself into every accessible habitat, 
spreads until it reaches limits that are for the time insur- 

§ 107. We pass now to the distribution of organic forms 
in Time. Geological inquiry has established the truth, that 
during a Fast of immeasurable duration, plants and animals 
have existed on the Earth. In all countries their buried 
remains are found in greater or less abundance. From com- 
paratively small areas, multitudinous different forms have been 
exhumed. Every exploration of new areas, and every closer 
inspection of areas already explored, brings more such forms 
to light. And beyond question, an exhaustive examination of 
all exposed strata, and of all strata now covered by the sea, 
would disclose forms immensely out-numbering all those at 
present known. Further, it is now becoming manifest to 
geologists, that even had we before us every kind of fossil 
which exists, we should still have nothing like a complete 
index to the past inhabitants of our globe. It has been long 
known that many sedimentary deposits have been so altered 
by the heat of adjacent molten matter, as greatly to obscure 
the organic remains contained in them. The extensive form- 
ations once called " transition," and now re-named " meta- 
morphic," are acknowledged to be formations of sedimentary 
origin, from which all traces of such fossil as they probably 
included, have been obliterated by igneous action. And the 
conclusion forcing itself into acceptance, is, that igneous rock 


has everywhere resulted from the complete melting-up of 
beds of detritus, originally deposited by water. How long the 
reactions of the Earth's molten nucleus on its cooled crust, 
have been thus destroying the records of Life which this cooled 
crust entombed, it is impossible to say ; but there are strong 
reasons for believing that the records which remain, bear but 
a small ratio to the records which have been destroyed. Thus 
we have but extremely-imperfect data for any conclusions 
respecting the distribution of organic forms in Time. Some 
few generalizations, however, may be regarded as established. 

One is, that the plants and animals now existing, mostly 
differ from the plants and animals which have existed. 
Though there are species common to our present Fauna and 
to past Faunas ; yet the fades of our present Fauna differs, 
more or less, from the fades of each past Faima. On carry- 
ing out the comparison, we find that past Faunas differ from 
each other ; and that the differences between them are pro- 
portionate to their degrees of remoteness from each other in 
Time, as measured by their relative positions in the sediment- 
ary series. So that if we take the assemblage of organic 
forms living now, and compare it with the successive assem- 
blages of organic forms that have lived in successive geologic 
epochs, we find that the farther we go back into the past, the 
greater does the imlikeness become : the number of species 
and genera common to the compared assemblages, becomes 
smaller and smaller ; and the assemblages differ more and 
more in their general characters. Though a species of 
brachiopod now extant, is almost identical with a species 
found in Silurian strata, and though between the Silurian 
Faima and our own, there are sundry common genera of mol- 
luscs ; it .is still undeniable that there is a proportion between 
lapse of time and divergence of organic forms. 

This divergence is comparatively slow and continuous, 
where there is continuity in the geological formations ; but is 
sudden and comparatively wide, wherever there occurs a 
great break in the succession of strata. The contrasts which 



thus arise gradually or all at once, in formations that are 
continuous or discontinuous^ are of two kinds. Faunas of 
different eras, are distinguished partly by the absence from 
one of types that are present in the other ; and partly by the 
unlikenesses between the types that are common to both. 
Such distinctions between Faunas as are due to the appear- 
ance or disappearance of types^ are of secondary significance : 
they possibly^ or probably, do not imply anything more than 
migrations or extinctions. The most significant distinctions 
are those between successive groups of organisms of the same 
type. And among such, as above said, the differences that 
arise are, speaking generally, small and continuous where a 
series of conformable strata gives proof of continued existence 
of the type in the locality ; while they are comparatively 
large and abrupt, where there is evidence that between the 
deposit of the adjacent formations, a long period elapsed. 

Another general fact, referred to by Mr Darwin as one 
which palaaontology has made tolerably certain, is that forms 
and groups of forms which have once disappeared from the 
Earth, do not reappear. Some few species and a good many 
genera, have continued throughout the whole period geologi- 
cally recorded. But omitting these as exceptional, it may be 
said that each species after arising, spreading for an era, and 
continuing abundant for an era, eventually declines and be- 
comes extinct ; and that similarly, each genus during a longer 
period increases in the number of its species, and during a 
longer period dwindles and at last dies out. Having made 
its exit, neither species nor genus ever re- enters. And the 
like is true, even of those larger groups called orders. Four 
types of reptiles that were once abundant, have not been 
found in modem formations, and do not at present exist. 
Though nothing less than an exhaustive examination of all 
strata, can prove conclusively that a special or general form of 
organization when once lost is never reproduced ; yet so 
many facts point to this inference, that its truth can scarcely 
be doubted. 


To form a conception of the total amount and general 
direction of the change that has arisen in organic forms during 
the geologic time measured by our sedimentary series, is at 
present impossible — the data are insufficient. The immense 
contrast between the few and low forms of the earliest-known 
Fauna, and the many and high forms of our existing Fauna, 
has been commonly supposed to prove, not only great 
change but great progress. Nevertheless, this appearance 
of progress may be, and probably is, mainly illusive. 
Wider knowledge and increased power of interpretation, have 
made it manifest that remains of comparatively well-organized 
creatures, really existed in strata long supposed to be devoid 
of them ; and that where they are actually absent, the nature 
of the strata often supplies a sufficient explanation of their 
absence, without assuming that they did not exist when these 
strata were formed. It has now become a tenable hypothesis, 
that the successively-higher types fossilized in our successive- 
ly-later deposits, indicate nothing more than successive migra- 
tions from pre-existing continents, to continents that were 
step by step emerging from the ocean — migrations which 
necessarily began with the inferior orders of organisms, and 
included the successively-superior orders as the new lands 
became more accessible to them, and better fitted for them.* 

While the evidence usually supposed to prove progres- 
sion, is thus imtrustworthy, there is trustworthy evidence 
that there has been, in many cases, little or no progression. 
Though the types which have existed from palaeozoic and me- 
sozoic times down to the present day, are almost universally 
changed ; yet a comparison of ancient and modem members 
of these types, shows that the total amount of change is not 
relatively great, and that it is not manifestly towards a higher 
organization. Though nearly all the living forms which have 
prototypes in early formations, differ from these prototypes 
specifically, and in most cases generically ; yet ordinal pecu- 
liarities are, in very numerous cases, maintained from the earli- 

• For explanations, seo " Illogical Geology." Ssmya : Second Series, 
21 * 


est times geologically recorded, down to our own time; and we 
have no visible evidence of superiority in the existing genera 
of these orders. In his lecture " On the Persistent Types of 
Animal Life/' Prof. Huxley enumerated many cases. On 
the authority of Dr Hooker, he stated " that there are Carbon- 
iferous plants which appear to be generically identical with 
some now living ; that the cone of the Oolitic Araucaria is 
hardly distinguishable from that of an existing species ; that a 
true Ptnm appears in the Purbecks and a Juglana in the chalk." 
Among animals he named palseozoic and mesozoic corals 
which are very like certain extant corals ; genera of Silurian 
molluscs that answer to existing genera ; insects and arach- 
nids in the coal formations, that are not more than generically 
different from some of our own insects and arachnids. He in- 
stanced "the Devonian and Carboniferous Pleuracanihus, 
which differs no more from existing sharks than these do 
from one another ;" early mesozoic reptiles " identical in the 
essential characters of their organization with those now liv- 
ing ;" and Triassic mammak which did not differ " nearly so 
much from some of those which now live, as these differ from 
one another." Continuing the argument in his " Aniiiversary 
Address to the Geological Society " in 1862, Prof. Huxley 
gave many cases in which the changes that have taken place, 
are not changes towards a more specialized or higher organ- 
ization — asking " in what sense are the Liassic Chelonia infe- 
rior to those which now exist P How are the Cretaceous 
Ichthyosauria, Plesiosauria, or Pterosauria less embryonic 
or more differentiated species than those of the Lias P " 
While, however, contending that in most instances " positive 
evidence fails to demonstrate any sort of progressive modifi- 
cation towards a less embryonic or less generalized type in a 
great many groups of animals of long-continued geological 
existence ; " Prof. Huxley added, that there are other groups 
" co-existing with them, under the same conditions, in which 
more or less distinct indications of such a process seem to be 
traceable." And in illustration of this, he named thut better 


development of the vertebrae which characterizes some of 
the more modern fishes and reptiles, when compared with an- 
cient fishes and reptiles of the same orders ; and the " regu- 
larity and evenness of the dentition of the Anoplotheriiim as 
contrasting with that of existing Artiodactyles." 

The facts thus summed up, do not show that higher forms 
have not arisen on the Earth in the course of geologic time, 
any more than the facts commonly cited prove that higher 
forms have arisen ; nor are they regarded by Prof. Huxley 
as showing this. Were the types which have survived from 
palaeozoic and mesozoic periods down to our own day, the 
only types ; and did the modifications, rarely of more than 
generic value, which these types have undergone, give no 
better evidences of increased complexity than are actually 
given by them ; then it would be inferable that there has 
been no appreciable advance among organic forms. But 
there now exist, and have existed during the more recent 
geologic epochs, various tjrpes which are not known to have 
existed in earlier epochs — some of them widely unlike 
these persistent types, and some of them nearly allied to 
these persistent types. As yet, we know nothing respecting 
the origins of these new types. But it is quite possible that 
causes like those which have produced generic differences in 
the persistent types, may, in some or many cases, have pro- 
duced modifications great enough to constitute ordinal difier- 
ences — ^may have resulted in the formation of tj^pes that are 
now classed as separate. If structural contrasts not exceed- 
ing certain moderate limits, are held to mark only generic 
distinctions ; and if organisms displaying larger structural 
contrasts are considered ordinally or typically distinct ; it is 
clear that the persistence of a given type through a long 
geologic period without apparently undergoing deviations of 
more than generic value, by no means disproves the occurrence 
of far greater deviations ; since the forms resulting from such 
far greater deviations, being regarded as typically distinct 
forms, will not be taken as evidence of great change in the 


original type. That which Prof. Huxley's argument proyes^ 
and that only which he considers it to prove, is that organisms 
have no innate tendencies to assume higher forms, and that 
*^ any admissible hypothesis of progressive modification, must 
be compatible with persistence without progression through 
indefinite periods.'' 

One very significant fact must be added, concerning the 
relation between distribution in Time and distribution in 
Space. I quote it from Mr Darwin : — " Mr Clift many years 
ago showed that the fossil mammals from the Australian 
caves were closely allied to the living marsupals of that con- 
tinent. In South America, a similar relationship is manifest, 
even to an imeducated eye, in the gigantic pieces of armour 
like those of the armadillo, found in several parts of La Plata ; 
and Professor Owen has shown in the most striking manner 
that most of the fossil mammals, buried there in such num- 
bers, are related to the South American types. This relation- 
ship is even more clearly seen in the wonderful collection of 
fossil bones made by MM. Lund and Clausen in the caves of 
Brazil. I was so much impressed with these facts that I 
strongly insisted, in 1839 and 1845, on this * law of the suc- 
cession of types,' — on 'this wonderful relationship in the 
same continent between the dead and the living.' Professor 
Owen has subsequently extended the same generalization to the 
mammalB of the Old World. We see the same law in this 
author's restorations of the extinct and gigantic birds of New 
Zealand. We see it also in the birds of the caves of Brazil. 
Mr Woodward has shown that the same law holds good, with 
sea-shells, but from the wide distribution of most genera of 
molluscs, it is not well displayed by them. Other cases could 
be added, as the relation between the extinct and living land- 
shells of Madeira ; and between the extinct and living brack- 
ish-water shells of the Aralo-Caapian Sea."* 

The general results then, are these. Our knowledge of 
distribution in Time, being derived wholly from the evidence 
afforded by fossils, is limited to that geologic time of which 


some records remain: cannot extend to those pre-geologic 
times the records of which have been obliterated. From 
these remaining records, which probably form but a small 
fraction of the whole, the general facts deducible are : — That 
such organic types as have lived through successive epochs, 
have almost universally undergone modifications of specific 
and generic values — ^modifications which have commonly been 
great in proportion as the period has been long. That besides 
the types that have persisted from ancient eras down to our 
own era, other types have from time to time made their ap- 
pearance in the ascending series of our strata — types of which 
some are lower and some higher than the types previously 
recorded ; but whence these new types came, and whether 
any of them arose by divergence from the previously-recorded 
types, the evidence does not yet enable us to say. That in 
the course of long geologic epochs, nearly all species, most 
genera, and a few orders, become extinct ; and that a species, 
genus, or order, which has once disappeared from the Earth, 
never reappears. And, lastly, that the Fauna now occupying 
each separate area of the Earth's surface, is very nearly allied 
to the Fauna which existed on that area during recent geolo- 
gic times. 

§ 108. Omitting sundry minor generalizations, the exposi- 
tion of which would involve too much detail, what is to be 
said of these major generalizations ? 

The distribution in Space cannot be said to imply that or- 
ganisms have been designed for their^articular habitats, and 
placed in them ; since, besides the habitat in which an organ- 
ism is found there are commonly other habitats, as well or 
better for it, from which it is absent — ^habitats to which it 
is so much better fitted than organisms now occupying them, 
that it extrudes these organisms when allowed the oppor- 
tunity. Neither can we suppose that one end has been to 
establish varieties of Floras and Faunas ; since, if so, why are 
the Floras and Faimas but little divergent in widely-sundered 


areas between which migration is possible, while they are 
markedly divergent in adjacent areas between which migra- 
tion is impossible P 

Passing to distributions in Time, there arise the questions 
— ^why during nearly the whole of that vast period geological- 
ly recorded, have there existed none of those highest organic 
forms which have now overrun the Earth ? — how is it that we 
find no traces of a creature endowed with large capacities for 
knowledge and happiness P The answer that the Earth was 
not, in remote times, a fit habitation for such a creature, be- 
sides being unwarranted by the evidence, suggests the equally 
awkward question — why during untold millions of years did the 
Earth remain fit only for inferior creatures P What, again, is 
the meaning of this extinction of types P To conclude that 
the saurian type was replaced by other types at the beginning 
of the tertiary period, because this type was not adapted to 
the conditions which then arose, is to conclude that this type 
could not be modified into fitness for the conditions ; and this 
conclusion is quite at variance with the hypothesis that creative 
skill is shown in the multiform adaptations of one type to 
many ends. 

What interpretations may rationally be put on these and 
other general facts of distribution in Space and Time, we 
shall see in the next division of this work ; to which let us 
now pass. 





§ 109. In the foregoing Part, we have contemplated the 
most important of the generalizations to which biologists 
have been led by observation of organisms. These Induc- 
tions of Biology have also been severally glanced at on their 
deductive sides ; for the purpose of noting the harmony that 
exists between them, and those primordial truths set forth in 
First Principles, Having thus studied the leading pheno- 
mena of life separately, we are prepared for studying them in 
their ensemble^ with the view of arriving at the most general 
interpretation of them. 

There is an ensemble of vital phenomena presented by each 
organism in the course of its growth, development, and decay ; 
and there is an ensemble of vital phenomena presented by 
the organic world as a whole. Neither of these can be 
properly dealt with apart from the other. But the last of 
them may be separately treated more conveniently than the 
first. What interpretation we put on the facts of structure 
and function in each living body, depends entirely on our 
conception of the mode in which living bodies in general 
have originated. To form some conclusion respecting this 
mode — a provisional if not a permanent conclusion — must 
therefore be our first step. 

We have to choose between two hypotheses — ^the hypo- 
thesis of Special Creation and the hypothesis of Ei^olution. 


Either the multitudinous kinds of organisms that now exist, 
and the still more multitudinous kinds that haVe existed 
during past geologic eras, have been from time to time separ- 
ately made ; or they have arisen by insensible steps, through 
actions such as we see habitually going on. Both hypo- 
theses imply a Cause. The last, certainly as much as the 
first, recognizes this Cause as inscrutable. The point at 
issue is, how this inscrutable Cause has worked in the pro- 
duction of living forms. This point, if it is to be decided at 
all, is to be decided only by examination of evidence. Let 
us inquire which of these antagonist hypotheses is most con- 
gruous with established facts. 



§ 110. Early ideas are not usually true ideas. Unde- 
veloped intellect, be it that of an individual or that of the 
race, forms conclusions which require to be revised and re- 
revised, before they reach a tolerable correspondence with 
realities. Were it otherwise, there would be no discovery, no 
increase of intelligence. What we call the progress of 
knowledge, is the bringing of Thoughts into harmony with 
Things ; and it implies that the first Thoughts are either 
wholly out of harmony with Things, or in very incomplete 
harmony with them. 

If illustrations be needed, the history of every science 
Aimishes them. The primitive notions of mankind as to the 
structure of the heavens, were wrong; and the notions 
which replaced them were successively less wrong. The 
original belief respecting the form of the Earth was wrong ; 
and this wrong belief survived through the first civilizations. 
The earliest ideas that have come down to us concerning the 
natures of the elements were wrong ; and only in quite 
recent times has the composition of matter in its various 
forms been better understood. The interpretations of me- 
chanical facts, of meteorological facts, of physiological facts, 

* Several of the arguments used in this chapter and in that which follows it, 
formed parts of an essay on " the Derelopment Hypothesis," originally published 
in 1852. 


were at first wrong. In all these cases men set out with 
beliefs wliicli, if not absolutely false, contained but small 
amounts of truth disguised by immense amoimts of error. 

Hence the hypothesis that living beings resulted from 
special creations, being a primitive hypothesis, is probably 
an untrue hypothesis. If the interpretations of Nature given 
by aboriginal men, were erroneous in other directions, they 
were most likely erroneous in this direction. It would bo 
strange if, while these aboriginal men failed to reach the truth 
in so many cases where it is comparatively conspicuous, 
they yet reached the truth in a case where it is compara- 
tively hidden. 

§ 111. Besides the improbability given to the belief in 
special creations, by its association with mistaken early 
beliefs in general ; a ftirther improbability is given to it by 
its association with a special class of mistaken belie&. It 
belongs to a family of beliefs which have one after another 
been destroyed by advancing knowledge; and is, indeed, 
almost the only member of the family that survives among 
educated people. 

.We aU know that the savage thinks of each striking phe- 
nomenon, or group of phenomena, Ba caused by some separate 
personal agent ; that out of this fetishistic conception there 
grows up a polytheistic conception, in which these minor per- 
sonalities are variously generalized into deities presiding over 
different divisions of nature ; and that these are eventually 
further generalized. This progressive consolidation of causal 
agencies, may be traced in the creeds of all races ; and is 
far from complete in the creeds of the most advanced races. 
The unlettered rustics who till our fields, do not let the con- 
sciousness of a supreme power whcdly absorb the aboriginal 
conceptions of good and evil spirits, and charms or secret 
potencies dwelling in particular objects. The earliest mode 
of thinking changes, only as fast as the constant relations 
among phenomena are established. Scarcely less 


familiar is the tmtli, that while accumulating knowledge 
makes these conceptions of personal causal agents gradually 
more vague, as it merges them into general causes, it also 
destroys the habit of thinking of them as working after the 
methods of personal agents. We do not now, like Kepler, 
assimie guiding spirits to keep the planets in their orbits. 
It is no longer the universal belief that the sea was once for 
all mechanically parted from the dry land; or that the 
mountains were placed where we see them by a sudden cre- 
ative act. All but a narrow class have ceased to suppose 
sunshine and storm to be sent in some arbitrary succession. 
The majority of educated people have given up thinking of 
epidemics as punishments inflicted by an angry deity. Nor 
do even the common people regard a madman as one pos- 
sessed by a demon. That is to say, we everjrwhere see 
fading away the anthropomorphic conception of the Un- 
known Cause. In one case after another, is abandoned that 
interpretation which ascribes phenomena to a will analogous 
to the human will, working by methods analogous to human 

If, then, of this once-numerous family of beliefs, the im- 
mense majority have become extinct, we may not unrea- 
sonably expect that the few remaining members of the f^imily 
will become extinct. One of these is the belief we are here 
considering — ^the belief that each species of organism was 
specially created. Many who in all else have abandoned 
the aboriginal theory of things, still hold this remnant of the 
aboriginal theory. Ask any tolerably-informed man whether 
he accepts the cosmogony of the Indians, or the Greeks, or 
the Hebrews, and he will regard the question as next to an 
insult. Yet one element common to these cosmogonies he 
very likely retains: not bearing in mind its origin. For 
whence did he get the doctrine of special creations P Catechise 
him, and he is forced to confess that it was put into his mind 
in childhood, as one portion of a story which, as a whole, he 
has long since rejected. Why this fragment is likely to bo 


right while all the rest is wrong, he is unable to say. May 
we not then expect, that the relinquishment of all other 
parts of this story, wiU bye and bye be followed by the 
relinquishment of this remaining part of it P 

§ 112. The belief which we find thus questionable, both 
as being a primitiye belief and as being a belief belonging to 
an almost-extinct family, is a belief that is not countenanced 
by a single fact. No one oyer saw a special creation ; no 
one ever found proof of an indirect kind, that a special 
creation had taken place. It is significant, as Dr Hooker 
remarks, that naturalists who suppose new species to be 
miraculously originated, habitually suppose the origination 
to occur in some region remote from human observation. 
Wherever the order of organic nature is exposed to the view of 
zoologists and botanists, it expels this conception ; and the 
conception survives only in connexion with imagined places, 
where the order of organic phenomena is unknown. 

Besides being absolutely without evidence to give it exter- 
nal support, this hypothesis of special creations cannot sup- 
port itself internally — cannot be framed into a coherent 
thought. It is one of those illegitimate symbolic concep- 
tions, so continually mistaken for legitimate symbolic concep- 
tions {First Principles, § 9), because they remain untested. 
Immediately an attempt is made to elaborate the idea into 
anything like a definite shape, it proves to be a pseud-idea, 
admitting of no definite shape. Is it supposed that a new 
organism, when specially created, is created out of nothing P 
If so, there is a supposed creation of matter ; and the crea- 
tion of matter is inconceivable — ^implies the establishment of 
a relation in thought between nothing and something — a 
relation of which one term is absent — ^an impossible rela- 
tion. Is it supposed that the matter of which the new or- 
ganism consists, is not created for the occasion, but is taken 
out of its pre-existing forms and arranged into a new form P If 
so, we are met by the question — ^how is the re-arrangement 


effected P Of the myriad atoms going to the composition of 
the new organism, all of them previonsly dispersed through 
the neighbouring air and earth, does each, suddenly dis- 
engaging itself from its combinations, rush to meet the rest, 
unite with them into the appropriate chemical compounds, 
and then fall with certain others into its appointed place in 
the aggregate of complex tissues and organs P Surely thus 
to assume a myriad supernatural impulses, differing in their 
directions and amounts, given to as many different atoms, is a 
multiplication of mysteries rather than the solution of a 
mystery. For every one of these impulses, not being the 
result of a force locally existing in some other form, implies 
the creation of force ; and the creation of force is just as 
inconceivable as the creation of matter. And thus is it with 
all attempted ways of representing the process. The old 
Hebrew idea that God takes clay and moulds a new creature, 
as a potter might mould a vessel, is probably too grossly an- 
thropomorphic to be accepted by any modem defender of the 
special-creation doctrine. But having abandoned this crude 
belief, what beKef is he prepared to substitute P If a new 
organism is not thus produced, then in what way is a new 
organism produced P or rather — in what way can a new 
organism be conceived to be produced P We will not ask for 
the ascertained mode, but will be content with a mode 
that can be consistently imagined. No such mode, however, 
is assignable. Those who entertain the proposition that each 
kind of organism results from a divine interposition, do so 
because they refrain from translating words into thoughts. 
The case is one of those where men do not really believe, but 
rather belisve they believe. For belief, properly so called, 
implies a mental representation of the thing believed ; and 
no such mental representation is here possible. 

§ 113. If we imagine mankind to be contemplated by 
some creature as short-lived as an ephemeron, but possessing 
intelligence like our own — if we imagine such a being study- 



ing men and women, during Iiis few hours of life, and 
speculating as to the mode in which they came into existence ; 
it is manifest that, reasoning in the usual way, he would 
suppose each man and woman to have been separately 
created. No appreciable changes of structure occurring in 
any of them during the few hours over which his observa- 
tions extended, this being would probably infer that no 
changes of structure were taking place, or had taken place ; 
and that from the outset, each man and woman had pos- 
sessed all the characters then visible — had been orginally 
formed with them. This would naturally be the first im- 
pression. The application is obvious. A himian life 
is ephemeral compared with the life of a species ; and even 
the period over which the records of human experience 
extend, is ephemeral compared with the life of a species. 
There is thus a parallel contrast between the immensely-long 
series of changes that have occurred during the life of a 
species, and that small portion of the series open to our view. 
And there is no reason to suppose that the first conclusion 
drawn by mankind from this small part of the series visible 
to them, is any nearer the truth, than would be the conclu- 
sion of the supposed ephemeral being respecting men and 

This analogy, suggesting as it does how the hypothesis of 
special creations is merely a formula for our ignorance, raises 
the question — ^what reason have we to assume special crea- 
tions of species but not of individuals ; unless it be that in 
the case of individuals we directly know the process to be 
otherwise, but in the case of species do not directly know it 
to be otherwise ? Have we any ground for concluding that 
species were specially created, except the ground that we 
haye no immediate knowledge of their origin ? And does our 
ignorance of the manner in which they arose, warrant us in 
asserting that they arose by special creation P 

Another question is suggested by this analogy. Those 
who, in the absence of immediate evidence of the way in 


whicli species arose, assert that they arose not in any way 
analogous to that in which individuals arise, but in a totally 
distinct way, think that by this supposition they honour the 
Unknown Cause of things ; and they oppose any antagonist 
doctrine as amounting to an exclusion of divine power from 
the world. But if divine power is demonstrated by the 
separate creation of each species, would it not have been still 
better demonstrated by the separate creation of each indivi- 
dual P Why should there exist this process of natural gene- 
sis ? Why should not omnipotence have been proved by the 
supernatural production of plants and animals everjrwhere 
throughout the world from hour to hour P Is it replied that 
the Creator was able to make individuals arise from one 
another in a natural succession, but not to make species thus 
arise P This is to assign a limit to power instead of magni- 
fying it. Is it replied that the occasional miraculous origina- 
tion of a species was practicable, but that the perpetual miracu- 
lous origination of cotmtless individuals was impracticable P 
This also is a derogation. Either it was possible or not pos- 
sible to create species and individuals aftier the same general 
method. To say that it was not possible is suicidal in those 
who use this argument ; and if it was possible, it is required 
to say what end is served by the special creation of species 
that would not have been better served by the special creation 
of individuals. Again, what is to be thought of the 

fact that the great majority of these supposed special creations 
took place before mankind existed P Those who think that di- 
vine power is demonstrated by special creations, have to answer 
the question — ^to whom demonstrated P Tacitly or avowedly, 
they regard the demonstrations as being for the benefit of 
mankind. But if so, to what purpose were the millions 
of these demonstrations which took place on the Earth when 
there were no int^Uigent beings to contemplate them P Did 
the Unknowable thus demonstrate his power to himself P 
Few will have the hardihood to say that any such demon- 
stration was needful. There is no choice but to regard them, 



either as superfluons exercises of power, which is a derogatory 
supposition, or as exercises of power that were necessary 
because species could not be otherwise produced, which is 
also a derogatory supposition. 

§ 114. Those who espouse the hypothesis of special ere* 
ations, entangle themselves in other theological difficulties. 
This assumption that each* kind of organism was specially 
designed, carries with it the implication that the designer 
intended everything that results from the design. There is 
no escape from the admission, that if organisms were severally 
constructed with a view to their respective ends; then 
the character of the constructor is indicated both by the 
ends themselves, and the perfection or imperfection with 
which the organisms are fitted to them. Observe the con- 

Without dwelling on the question put in a recent chap- 
ter, why during untold millions of years there existed on 
the Earth no beings endowed with capacities for wide 
thought and high feeling, we may content ourselves with 
asking why, at present, the Earth is largely peopled by 
creatures which inflict on each other, and on themselves, so 
much suffering ? Omitting the human race, whose defects 
and miseries the current theology professes to account for, 
and limiting ourselves to the lower creation, what must we 
think of the countless different pain-inflicting appliances 
and instincts with which animals are endowed ? Not only 
now, and not only ever since men have lived, has the Earth 
been a scene of warfare among all sentient creatures ; but 
palaeontology shows us that, from the eeu^liest eras geologi- 
cally recorded, there has been going on this universal cam- 
age. Fossil structures, in common with the structures of 
existing animals, show us elaborate weapons for destroying 
other animals. We have unmistakable proof that through- 
out all past time, there has been a perpetual preying of the 
superior on the inferior — a ceaseless devouring of the weak 


by the strong. How is this to be explained P How happens 
it that animals were so designed as to render this bloodshed 
necessary P How happens it that in almost every species, the 
number of individuals annually bom is such that the ma- 
jority die of starvation or by violence before arriving at ma- 
turity P Whoever contends that each kind of animal was 
specially designed, must assert either that there was a deli- 
berate intention on the part of the Creator to produce these 
results, or that there was an inability to prevent them. 
Which alternative does he prefer P To cast an imputation on 
the divine character, or assert a limitation of the divine 
power P It is useless for him to plead that the destruction of 
the less powerful by the more powerful, is a means of pre- 
venting the miseries of decrepitude and incapacity, and 
therefore works beneficently. For even were the chief mor- 
taKty among the aged instead of among the young, there 
would still arise the unanswerable question — ^why were not 
animals constructed in such ways as to avoid these evils P 
why were not their rates of multiplication, their degrees of 
intelligence, and their propensities, so adjusted that these 
sufferings might be escaped P And if decline of vigour was 
a necessary accompaniment of age, why was it not provided 
that the organic actions should end in sudden death, when- 
ever they fell below the level required for pleasurable exist- 
ence P Will any one who contends that organisms were 
specially designed, assert that they could not have been 
designed so as to prevent suffering P And if he admits that 
they could have been made so as to prevent suffering, will 
he assert that the Creator preferred so making them as to 
inflict suffering P 

Even as thus presented, the difficulty is sufficiently great ; 
but it appears immensely greater when we examine the facts 
more closely. So long as we contemplate only the preying 
of the superior on the inferior, some good appears to be 
extracted from the evil — ^a certain amount of life of a higher 
order, is supported by sacrificing a great deal of life of a 


lower order. So long, too, as we leave out all mortality but 
that which, by carrying off the least perfect members of each 
species, leaves the most perfect members to continue the 
species ; we see some compensating benefit reached through 
the suffering inflicted. But what shall we say on finding 
innumerable cases in which the suffering inflicted brings no 
compensating benefit P What shall we say when we see the 
inferior destroying the superior? What shall we say on 
discovering elaborate appliances for securing the prosperity 
of organisms incapable of feeling, at the expense of misery 
to organisms capable of happiness P 

Of the animal kingdom as a whole, more than half the 
species are parasites. ''The number of these parasites,'' 
says Prof. Owen, *' may be conceived when it is stated that 
almost every known animal has its peculiar species, and 
generally more than one, sometimes as many as, or even 
more kinds than, infest the human body.'' Passing over the 
evils thus inflicted on animals of inferior dignity, let us limit 
ourselves to the case of man. The Bothriocepkulus latus 
and the TcBnia Boliumy are two kinds of tape-worm, which 
flourish in the human intestines ; producing great constitu- 
tional disturbances, sometimes ending in insanity ; aCid from 
the germs of the Tomia, when carried into other parts of the 
body, arise certain partially-developed forms known as Ch/sti- 
cerci, Echtnococei, and Ccsnuri, which cause disorganization 
more or less extensive in the brain, the lungs, the liver, 
the heart, the eye, &c., often ending fatally after long- 
continued suffering. Five other parasites, belonging to 
a different class, are found in the viscera of man — the 
TrichocephaluSy the Oxyuris, the Strongylua (two species), 
the Ancyhstomum, and the Ascaria; which, beyond that 
defect of nutrition which they necessarily cause, sometimes 
induce certain irritations that lead to complete demoraliza- 
tion. Of another class of entozoa, belonging to the sub- 
division Trematoda, there are five kinds found in different 
organs of the human body — ^the Uver and gall ducts, the 


portal vein, the intestine, the bladder, the eye. Then we 
have the Trichina spiralis^ which passes through one phase of 
its existence imbedded in the muscles and through another 
phase of its existence in the intestine ; and which, by the 
induced disease Trichmiads, has lately committed such ra- 
vages in Germany, as to cause a panic. And to these we 
must add the Guinea-worm, which in some part of Africa 
and India, makes men miserable by burrowing in their legs. 
From this list of entozoa, which is by no means complete, 
let us pass to the epizoa. There are two kinds of Acari, 
one of them inhabiting the follicles of the skin, and the 
other producing the itch. There are other creatures that 
bury themselves beneath the skin, and lay their eggs there ; 
and there are three species of lice which infest the surface of 
the body. Nor is this all : besides animal parasites, there 
are sundry vegetal parasites, which grow and multiply at 
our cost. The Scurcma ventriculi inhabits the stomach, and 
produces gastric disturbance. The Leptothrix huccalis is 
extremely general in the mouth, and may have something 
to do with the decay of teeth. And besides these, there are 
microscopic fungi which produce ringworm, porrigo, pityri- 
asis, thrush, &c. Thus the human body is the 
habitat of parasites, internal and external, animal and ve- 
getal, numbering, if all were set down, some two or three 
dozen species; sundry of which are peculiar to man, and 
many of which produce in man great suffering and not un- 
frequently death. What interpretation is to be put on these 
facts by those who espouse the hypothesis of special crea- 
tions? According to this hypothesis, all these parasites 
were designed with a view to their respective modes of life. 
They were endowed with constitutions fitting them to live 
by absorbing the juices of the human body ; they were fur- 
nished with appliances, often of a formidable kind, enabling 
them to root themselves in and upon the human body ; and 
they were made, prolific in an almost incredible degree, that 
their germs might have a sufiicient nimiber of chances of 


fmding their way into the human body. In short, elaborate 
contrivances were combined to insure the continuance of 
their respective races ; and to make it impossible for the suc- 
cessive generations of men to avoid being preyed upon by 
them. What shall we say to this arrangement P Shall we 
say that man, " the head and crown of things," was provided 
as a habitat for these parasites ? Or shall we say that these 
degraded creatures, incapable of thought or enjoyment, were 
created that they might cause imhappiness to manP One 
or other of these alternatives must be chosen by those who 
contend that every kind of organism was separately devised 
by the Creator. Which do they prefer P With the concep- 
tion of two antagonistic powers, which severally work good 
and evil in the world, the facts are congruous enough. But 
with the conception of a supreme beneficence, this gratuitous 
infliction of misery on man, in common with all other terres- 
trial creatures capable of feeling, is absolutely incompatible. 

§ 115. See then the results of our examination. The 
belief in special creations of organisms, is a belief that arose 
among men during the era of profoundest darkness ; and it 
belongs to a family of beliefs which have nearly all died out 
as enlightenment has increased. It is without a soUtary 
established fact on which to stand ; and when the attempt is 
made to put it into definite shape in the mind, it turns out to 
be only a pseud-idea. This mere verbal hypothesis, which 
men idly accept as a real or thinkable hypothesis, is of the 
same nature as would be one, based on a day's observation of 
human life, that each man and woman was specially created 
— ^an hypothesis not suggested by evidence, but by lack of 
evidence— an hypothesis which formulates absolute ignorance 
into a semblance of positive knowledge. Further, we see that 
this hypothesis, wholly without support, essentially inconceiv- 
able, and thus failing to satisfy men's intellectual need of an 
interpretation, fails also to satisfy their moral sentiment. 
It is quite inconsistent with those conceptions of the divine 


nature which they profess to entertain. If infinite power 
was to be demonstrated, then, either by the special creation 
of every individual, or by the production of species after a 
method akin to that in which individuals are produced, it 
would be better demonstrated than by the use of the two 
methods which the hypothesis assumes to be necessary. And 
if infinite goodness was to be demonstrated, then, not only 
do the provisions of organic structure, if they are especially 
devised, fail to demonstrate it ; but there is an enormous 
mass of them which imply malevolence rather than bene- 

Thus, however regarded, the h3rpothesis of special creations 
turns out to be worthless — worthless by its derivation; 
worthless in its intrinsic incoherence ; worthless as absolutely 
without evidence ; worthless as not supplying an intellectual 
need ; worthless as not satisfying a moral want. We must 
therefore consider it as coimting for nothing, in opposition 
to any other hypothesis respecting the origin of organic 



§ 116. Just as the supposition that races of organisms 
have been specially created, is discredited by its origin ; so, 
conversely, the supposition that races of organisms have 
been evolved, is credited by its origin. Instead of being 
a conception suggested and accepted when mankind were 
profoundly ignorant, it is a conception bom in times of com- 
parative enlightenment. Moreover, the belief that all organic 
forms have arisen in conformity with uniform laws, instead 
of through breaches of uniform laws, is a belief that has 
come into existence in the most-instructed class, living in 
these better-instructed times. Not among those who have 
paid no attention to the order of Nature, has this idea made 
its appearance ; but among those whose pursuits have famil- 
iarized them with the order of Nature. Thus the derivation 
of this modem hypothesis is as favourable as that of the 
ancient hypothesis is unfavourable. 

8 117. A kindred antithesis exists between the two fami- 
lies of beliefs, to which the beliefs we are comparing severally 
belong. While the one family has been dying out, the 
other family has been multiplying. Just as fast as men 
have ceased to regard different classes of phenomena as 
caused by special personal agents, acting irregularly ; so fast 
have they come to regard these different classes of phe- 
nomena as caused by a general agency acting uniformly — ^ihe 


two changes being correlative. And as, on the one hand, 
the hypothesis that each species resulted from a supernatural 
act, having lost nearly all its kindred hypotheses, may be 
expected soon to become extinct ; so, on the other hand, the 
hypothesis that each species resulted from the action of na- 
tural causes, being one of an ever-increasing family of hypo- 
theses, may be expected to survive and become established. 

Still greater will the probability of its survival and estab- 
lishment appear, when we observe that it is one of a particu- 
lar genus of hypotheses that has been rapidly extending. 
The interpretation of phenomena as resulting &om Evolution, 
has been independently showing itself in various fields of 
inquiry, quite remote from one another. The supposition 
that the Solar System has been gradually evolved out of dif- 
fused matter, is a supposition whoUy astronomical in its 
origin and application. Geologists, without being led thereto 
by astronomical considerations, have been step by step ad- 
vancing towards the conviction, that the Earth has reached 
its present varied structure through a process of Evolution. 
The inquiries of biologists have proved the falsity of the once 
general belief, that the germ of each organism is a minute 
repetition of the mature organism, differing from it only in 
bulk ; and they have shown, contrariwise, that every organ- 
ism, arising out of apparently-uniform matter, advances to its 
ultimate multiformity through insensible changes. Among 
philosophical politicians, there has been spreading the per- 
ception that the progress of society is an evolution: the 
truth that " constitutions are not made but grow," is a part 
of the more general truth that societies are not made but 
grow. It is now universally admitted by philologists, that 
languages, instead of being artificially or supematurally 
formed, have been developed. And the histories of religion, 
of philosophy, of science, of the fine arts, and of the indus- 
trial arts, show that these have passed through stages as un- 
obtrusive as those through which the mind of a child passes 
on its way to maturity. If^ then, the recognition of evolu- 


tion as the law of many diyerse orders of phenomena, has 
been spreading ; may we not say that there thence arises the 
probabiKty that evolution will presently be recognized as the 
law of the phenomena we are considering P Each further ad- 
vance of knowledge, confirms the belief in the unity of 
Nature ; and the discovery that evolution has gone on, or is 
going on, in so many departments of Nature, becomes a rea- 
son for believing that there is no department of Nature in 
which it does not go on. 

§ 118. The hypotheses of Special Creation and Evolution, 
are no less contrasted in respect of their legitimacy as hy- 
potheses. While, as we have seen, the one belongs to that 
order of sjrmbolic conceptions which are proved to be illusive 
by the impossibility of realizing them in thought ; the other 
is one of those symbolic conceptions which are more or less 
completely realizable in thought. The production of all 
organic forms by the slow accumulation of modifications upon 
modifications, and by the slow divergences resulting from 
the continual addition of diflferences to differences, is mentally 
representable in outline, if not in detail. Various orders of 
our experiences enable us to conceive the process. Let us 
look at one of the simplest. 

There is no apparent similarity between a straight line 
and a circle. The one is a curve ; the other is defined as 
without curvature. The one encloses a space ; the other 
will not enclose a space though produced for ever. The one 
is finite ; the other may be infinite. Yet, opposite as the 
two are in all their properties, they may be connected together 
by a series of lines no one of which differs from the adjacent 
ones in any appreciable degree. Thus, if a cone be cut by 
a plane at right angles to its axis, we get a circle. If, instead 
of being perfectly at right angles, the plane subtends with 
the axis an angle of 89° 59', we have an ellipse which no 
human eye, even when aided by an accurate pair of compasses, 
can distinguish from a circle. Decreasing the angle minute 


by minute, the ellipse becomes first perceptibly eccentric, then 
manifestly so, and by and by acquires so immensely elongated 
a form, as to bear no recognizable resemblance to a circle. 
By continuing this process, the ellipse changes insensibly into 
a parabola. On still further diminishing the angle, the para- 
bola becomes an hyperbola. And finally, if the cone be 
made gradually more obtuse, the hyperbola passes into a 
straight line, as the angle of the cone approaches 180°. Now 
here we have five different species of line — circle, ellipse, 
parabola, hyperbola, and straight line — each having its pecu- 
liar properties and its separate equation, and the first and 
last of which are quit^ opposite in nature, connected together 
as members of one series, all producible by a single process 
of insensible modification. 

But the experiences which most clearly illustrate to us 
the process of general evolution, are our experiences of 
special evolution, repeated in every plant and animal. Each 
organism exhibits^ within a short ' space of time, a series 
of changes which, when supposed to occupy a period inde- 
finitely great, and to go on in various ways instead of one 
way, give us a tolerably clear conception of organic evo- 
lution in general. In an individual development, we have 
compressed into a comparatively infinitesimal space, a series 
of metamorphoses equally vast with those which the hypo- 
thesis of evolution assimies to have taken place during those 
immeasurable epochs that the Earth's crust teUs us of. A 
tree differs from a seed immeasurably in every respect — 
in bulk, in structure, in colour, in form, in specific gravity, 
in chemical composition : differs so greatly that no visible 
resemblance of any kind can be pointed out between them. 
Yet is the one changed in the course of a few years into the 
other : changed so gradually, that at no moment can it be 
said — ^Now the seed ceases to be, and the tree exists. What 
can be more widely contrasted than a newly-born child and 
the small, semi-transparent, gelatinous spherule constituting 
the human ovum ? The infant is so complex in structure 


that a cyclopaedia is needed to describe its constituent parts. 
The germinal vesicle is so simple that it may be defined in 
a line. Nevertheless^ a few months suffice to develope the 
one out of the other ; and that, too, by a series of modifica- 
tions so small, that were the embryo examined at successive 
minutes, even a microscope would with difficulty disclose 
any sensible changes. Aided by such facts, the conception 
of general evolution may be rendered as definite a concep- 
tion as any of our complex conceptions can be rendered. If 
instead of the successive minutes of a child's foetal life, we 
take successive generations of creatures — ^if we regard the suc- 
cessive generations as differing from each other no more than 
the foetus did in successive minutes ; our imaginations must 
indeed be feeble if we fail to realize in thought, the evolu- 
tion of the most complex organism out of the simplest. If a 
single cell, under appropriate conditions, becomes a man in 
the space of a few years ; there can surely be no difficulty in 
tmderstanding how, under appropriate conditions, a cell may, 
in the course of untold millions of years, give origin to the 
human race. 

It is true that many minds are so unfamished with those 
experiences of Nature out of which this conception is built, 
that they find difficulty in forming it. Habitually looking 
at things rather in their statical than in their dynamical 
aspects, they never realize the fact that, by small increments 
of modification, any amount of modification may in time be 
generated. That surprise which they feel on finding one 
whom they last saw as a boy, grown into a man, becomes 
incredulity when the degree of change is greater. To such, 
the hypothesis that by any series of changes a protozoon 
should ever give origin to a mammal, seems grotesque — ^as 
grotesque as did Galileo's assertion of the Earth's movement 
seem to the Aristotleans ; or as grotesque as the assertion of 
the Earth's sphericity seems now to the New Zealanders. 
But those who accept a literally-unthinkable proposition as 


quite satisfactory, may not uimaturally be expected to make a 
converse mistake. 

§ 119. The liypothesis of evolution is contrasted with 
the hypothesis of special creations, in a further respect. It is 
not simply legitimate instead of illegitimate, because repre- 
sentable in thought instead of unrepresentable*; but it has 
the support of some evidence, instead of being absolutely 
unsupported by evidence. Though the facts at present as- 
signable in direct proof that by progressive modifications, 
races of organisms that are apparently distinct may result 
from antecedent races, are not sufficient ; yet there are nu- 
merous facts of the order required. It has been shown 
beyond all question that unlikenesses of structure gradually 
arise among descendants from the same stock. We find that 
there is going on a modifying process of the kind alleged as 
the source of specific differences : a process which, though 
slow in its action, does, in time, if the circumstances demand 
it, produce conspicuous changes — ^a process which, to aU 
appearance, would produce in the millions of years, and under 
the great varieties of conditions which geological records 
imply, any amount of change. 

In the chapters on " Heredity'* and "Variation," con- 
tained in the preceding Part, many such facts were given ; 
and plenty more might be added. Although comparatively 
little attention has been paid to the matter until recent times, 
the evidence already collected shows that there take place in 
successive generations, alterations of structure quite as 
marked as those which, in successive short intervals, arise in 
a developing embryo — ^nay, often much more marked ; since, 
besides differences due to changes in the relative sizes of 
parts, there sometimes arise differences due to additions and 
suppressions of parts. The structural modification proved 
to have taken place since organisms have been observed, is 
not less than the hypothesis demands — ^bears as great a ratio 


to tills brief period^ as the total amount of structural cHange 
seen in the evolution of a complex organism out of a simple 
germ, bears to that vast period during which living forms 
have existed on the Earth. 

We have, indeed, much the same kind and quantity of 
direct evidence that all organic beings have gradually arisen 
through the actions of natural causes, which we have that all 
the structural complexities of the Earth's crust have arisen 
through the actions of natural causes. It may, I think, be 
fairly said, that between the known modifications imdergoneby 
organisms, and the totality of modifications displayed in their 
structures, there is no greater disproportion than between the 
geological changes which have been witnessed, and the to- 
tality of geological changes supposed to be similarly caused. 
Here and there are pointed out sedimentary deposits now 
slowly taking place. At this place, it is proved that a shore 
has been encroached on by the sea to a considerable extent 
within recorded times ; and at another place, an estuary is 
known to have become shallower within the space of some 
generations. In one region a general upheaval is going on 
at the rate of a few feet in a century; while in another 
region occasional earthquakes are shown to cause slight 
variations of level. Appreciable amounts of denudation by 
water are visible in some localities ; and in other localities 
glaciers are detected in the act of grinding down the rocky sur- 
faces over which they glide. But the changes thus instanced, 
are infinitesimal compared with the aggregate of changes to 
which the Earth's crust testifies, even in its still extant sys- 
tems of strata. If, then, from the small changes now being 
wrought on the Earth's crust by natural agencies, we may 
legitimately conclude that by such natural agencies acting 
through vast epochs, all the structural complexities of the 
Earth's crust have been produced; may we not from the 
small known modifications produced in races of organisms 
by natural agencies, similarly infer that from natural agen- 


cies have slowly arisen all those structural complexities wMch 
we see in them P 

The hypothesis of Evolution then, has direct support from 
facts which, though small in amount, are of the kind required; 
and the proportion which these facts bear to the conclusion 
drawn, seems as great as is the proportion between facts and 
conclusion which, in another case, produces acceptance of the 

§ 120, Let us put ourselves for a moment in the position of 
those who, from their experiences of human modes of action, 
draw inferences respecting the mode of action of that ultimate 
power manifested to us through phenomena. We shall find 
the supposition that each kind of organism was separately 
designed and put together, to be much less consistent with 
their professed conception of this ultimate power, than is the 
supposition that all kinds of organisms have resulted from 
one unbroken process. Irregularity of method is a mark of 
weakness. Uniformity of method is a mark of strength. Con- 
tinual interposition to alter a pre-arranged set of actions, 
implies defective arrangement in those actions. The main- 
tenance of those actions, and the working out by them of the 
highest results, implies completeness of arrangement. If 
human workmen, whose machines as at first constructed 
require perpetual adjustment, show their increasing skill by 
making their machines self-adjusting ; then, those who figure 
to themselves the production of the world and its inhabitants 
by a " Great Artificer," must admit that the achievement of 
this end by a persistent process, adapted to all contingencies, 
implies greater skill than its achievement by the process of 
meeting the contingencies as they severally arise. 

So, too, it is with the contrast imder its moral aspect. We 
saw that to the hypothesis of special creations, a difficulty 
is presented by the absence of high forms of life during those 
immeasurable epochs of the Earth's existence which geology 



records. But to the hypothesis of evolution, this absence is 
no such obstacle. Suppose evolution, and this question is 
necessarily excluded. Suppose special creations, and this 
question, unavoidably raised, can have no satisfSactory an- 
swer. StiU more marked is this contrast between the 
two hypotheses, in presence of that vast amount of suf- 
fering entailed on all orders of sentient beings, by their 
imperfect adaptations to their conditions of life ; and the 
further vast amount of suffering entailed on them by enemies 
and by parasites. We saw that if organisms were severally 
designed for their respective places in Nature, the inevitable 
conclusion is, that these thousands of kinds of inferior organ- 
isms which prey upon superior organisms, were intended to 
inflict all the pain and mortality which results. But the hy- 
pothesis of evolution involves us in no such dilemma. Slowly, 
but surely, evolution brings about an increasing amount 
of happiness : all evils being but incidental. By its essen- 
tial nature, the process must everywhere produce greater 
fitness to the conditions of existence ; be they what they may. 
Applying alike to the lowest and the highest forms of organ- 
ization, there is in all cases a progressive adaptation ; and a 
survival of the most adapted. If, in the uniform working 
out of the process, there are evolved organisms of low types, 
which prey on those of higher types, the evils inflicted form 
but a deduction from the average benefits. The universal 
and necessary tendency towards supremacy and multiplica- 
tion of the best, applying to the organic creation as a whole 
as well as to each species, is ever diminishing the damage 
done — ^tends ever to maintain those most superior organisms 
which, in one way or other, escape the invasions of the infe- 
rior, and so tends to produce a type less liable to the inva- ; 
sions of the inferior. Thus the evils accompanying evcJu- i 
tion are ever being self-eliminated. Though there may arise I 
the question — Why could they not have been avoided? 
there does not arise the question — ^Why were they deliber- ^ 


ately inflicted? Whatever may be thouglit of them, it is 
clear that they do not imply gratuitous malevolence. 

§ 121. In all respects, then, the hypothesis of evolution 
contrasts favourably with the hypothesis of special creation. 
It has arisen in comparatively-instructed times, and in the 
most cultivated class. It is one of those beliefs in the uni- 
form concurrence of phenomena, which are gradually sup- 
planting beliefs in their ij'regular and arbitrary concurrence ; 
and it belongs to a genus of these beliefs which has of late 
been rapidly spreading. It is a definitely-conceivable hypo- 
thesis : being simply an extension to the organic world at 
large, of a conception built from our experiences of individual 
organisms ; just as the hypothesis of universal gravitation, 
was an extension of the conception which our experiences 
of terrestrial gravitation had produced. This d^nitely-con- 
ceivable hypothesis, besides the support of numerous ana- 
logies, has the support of direct evidence ; we have positive 
proof that there is going on a process of the kind alleged ; 
and though the results of this process, as actually witnessed, 
are minute in comparison with the totality of results ascribed 
to it, yet they bear to such totality, a ratio as great as that by 
which an analogous h3rpothesis is justified. Lastly, that senti- 
ment which the doctrine of special creations is thought neces- 
sary to satisfy, is much better satisfied by the doctrine of evolu- 
tion ; since this doctrine raises no contradictory implications 
respecting the Unknown Cause, such as are raised by the 
antagonist doctrine. 

And now, having observed how, under its most general 
aspects, the hypothesis of evolution commends itself to us, 
by its derivation, by its coherence, by its analogies, by its 
direct evidence, by its implications ; let us go on to consider 
the several orders of facts which yield indirect support to it. 
We will begin by noting the harmonies that exist between 
it, and sundry of the inductions set forth in Part II. 

23 ♦ 



§ 122. In § 103, we saw that the relations which exist 
among the species, genera, orders, and classes of organisms, 
are not interpretable as results of any such causes as have 
been usually assigned. We will here consider whether they 
are interpretable as the results of evolution. Let us first 
contemplate some familiar facts. 

The Norwegians, Swedes, Danes, Germans, Dutch, and 
Anglo-Saxons, form together a group of Scandinavian races, 
that are but slightly divergent in their characters. Welsh, 
Irish, and Highlanders, though they have diflPerences, have 
not differences such as to hide a decided community of na- 
ture : they are classed together as Celts. Between the 
Scandinavian race as a whole and the Celtic race as a 
whole, there is a recognized distinction greater than that 
between the sub-divisions which make up one or the other. 
And the several peoples inhabiting Southern Europe are more 
nearly allied to one another, than the aggregate they form is 
allied to the aggregates of Northern peoples. If, again, we 
compare these European varieties of man taken as a group, 
with that group of Eastern varieties which had a common 
origin with it, we see a stronger contrast than between the 
European varieties themselves. And once more, ethnolo- 
gists find differences of still higher importance, between the 
Aryan stock as a whole and the Mongolian stock as a whole, 


or the Negro stock as a whole. Though these contrasts 
are partially obscured by intermixtures ; yet they are not so 
obscured as to hide the truths that the most-nearly-allied 
varieties of man, are those which diverged from one ano- 
ther at a comparatively-recent period; that each group 
of nearly-allied varieties, is more strongly contrasted with 
other such groups that had a common origin with it at a 
remoter period; and so on, until we come to the largest 
groups, which are the most strongly contrasted, and of whose 
divergence no trace is extant. 

The relations existing among the classes and sub-elasses 
of languages, have been briefly referred to by Mr Darwin, in 
illustration of his argument. We know that languages have 
arisen by evolution. Let us then see what grouping of them 
evolution has produced. On comparing the dialects of adja- 
cent counties in England, we find that their diiferences are so 
small as scarcely to distinguish them. Between the dialects 
of the Northern counties taken together, and those of the 
Southern counties taken together, the contrast is stronger. 
These clusters of dialects, together with those of Scotland and 
Ireland, are nevertheless so similar, that we regard them as 
one language. The several languages of Scandinavian Eu- 
rope, including English, are much more unlike one ano- 
ther, than are the several dialects which each of them in- 
cludes ; in correspondence with the fact that they diverged 
from one another at earlier periods than did their respective 
dialects. The Scandinavian languages have nevertheless a 
certain community of character, which distinguishes them as a 
group from the languages of Southern Europe ; between 
which there are general and special affinities that similarly 
unite them into a group formed of sub-groups containing sub- 
sub-groups. And this wider divergence between the order 
of languages spoken in Northern Europe, and the order of 
languages spoken in Southern Europe, answers to the longer 
time that has elapsed since their differentiation commenced. 
Further, these two orders of modem European languages, as 


well as Latin and Greek and certain extinct and spoken 
languages of the East, are shown to have traits in 
common, which, notwithstanding the wide gaps between 
them, unite them together as one great class of Aryan lan- 
guages; radically distinguished from the classes of lan- 
guages spoken by the other great divisions of the human 

$ 123. Now this kind of subordination of groups, which 
we see arises in the course of continuous descent, multiplica- 
tion, and divergence, is just the kind of subordination of 
groups which plants and animals exhibit : it is just this 
kind of subordination which has thrust itself on the attention 
of naturalists, in spite of pre-conceptions. 

The original idea was that of arrangement in linear order. 
We saw that even after a considerable acquaintance with the 
structures of organisms had been acquired, naturalists con- 
tinued their eflforts to reconcile the facts with the notion of a 
uni-serial succession. The accumulation of evidence necessi- 
tated the breaking up of the imagined chain into groups 
and sub-groups. Gradually there arose the conviction that 
these groups do not admit of being placed in a line. And the 
conception finally arrived at, is, that of certain great sub- 
kingdoms, very widely divergent, each made up of classes 
much less widely divergent, severally containing orders still 
less divergent; and so on with genera and species. The 
diagram on page 303, shows the general relations of these 
divisions in their degrees of subordination. 

Hence this ''grand fact in natural history of the subordina- 
tion of group under group, which from its familiarity does 
not always sufficiently strike us," is perfectly in harmony 
with the hypothesis of evolution. The extreme significance 
of this kind of relation among organic forms, is dwelt on by 
Mr Darwin ; who shows how an ordinary genealogical tree 
represents, on a small scale, a system of grouping analogous to 
that which exists among organisms in general, and which is 


explained on the supposition of a genealogical tree by which 
all organisms are affiliated. If, wherever we can trace 
direct descent, multiplication, and divergence, this formation 
of groups within groups takes place ; there results a strong 
presumption that the groups within groups which constitute 
the animal and vegetal kingdoms, have arisen by direct 
descent, multiplication, and divergence — that is, by evolu- 

§ 124. Strong confirmation of this inference is furnished 
by the fact, that the more marked difierences which divide 
groups, are, in both cases, distinguished from the less 
marked difierences which divide sub-groups, by this, that 
they are not simply greater in degree, but they are more 
radical in kind. Objects, as the stars, may present them- 
selves in small clusters, which are again more or less aggre- 
gated into clusters of clusters, in such manner that the in- 
dividuals of each simple cluster, are much closer together 
than are the simple clusters composing a compound cluster : 
in which case, the kinship that unites groups of groups 
difiers from the kinship that unites groups, not in nature^ 
but only in amount. But this is not the case either with 
the groups and sub-groups which we know have resulted 
from evolution, or with those which we here infer have re- 
sulted from evolution. Among these, we find the highest 
or most gensral classes, are separated from one another by 
fundamental difierences that have no common measure with 
the difierences that separate small classes. Observe the pa-* 

We saw that each sub-kingdom of animals is marked off 
from the other sub-kingdoms, by a total unlikeness in its 
plan of organization : that is, the members of any sub-kingdom 
are bound together, not by some superficial attribute which 
they all have, but by some attribute determining the general 
nature of their organizations. While, contrariwise, the 
members of the smallest groups are united together, and se- 
parated from the members of other small groups, by modi- 


fications which do not affect the essential relations of parts. 
That this is just the kind of arrangement which results froir 
evolution, the case of languages will show. 

If we compare the dialects spoken in different parts of 
England, we find scarcely any differences but those of pro- 
nimciation : the structures of the sentences are almost 
uniform. Between English and the aUied modern languages, 
there are decided divergences of structure : there are some 
xmlikenesses of idiom ; some imlikenesses in the ways of 
modifying the meanings of verbs ; and considerable uinlike- 
nesses in the uses of genders. But these imlikenesses are not 
sufficient to hide a general community of organization. A 
greater contrast of structure exists between these modem lan- 
guages of Western Europe, and the classic languages. That 
differentiation into abstract and concrete elements, which is 
shown by the substitution of auxiliary words for inflections, 
has produced a higher specialization distinguishing these 
languages as a group from the older languages. Neverthe- 
less, both the ancient and modem languages of Europe, to- 
gether with some Eastern languages derived from the same 
original, have, imder all their differences of organization, a 
fundamental community of organization ; inasmuch as all of 
them exhibit the formation of words by such a coalescence 
and integration of roots as destroys the independent meanings 
of the roots. These Aryan languages, and others which 
have the amalgcumate character, are united by it into a class 
distinguished from the aptotic and agglutinate languages ; in 
which the roots are either not imited at all, or so incompletely 
united that one of them still retains its independent meaning. 
And philologists find that these fundamental differences which 
severally determine the grammatical forms, or modes of com- 
bining ideas, are really characteristic of the primary divisions 
among languages. 

That is to say, among languages, where we know that 
evolution has been going on, the greatest groups are marked 
off from one another by the strongest structural contrasts ; 
and as the like holds among groups of organisms, there re- 


suits a further reason for inferring that these have been 

§ 125. There is yet another paralleKsm of like meaning. 
We saw (§ 101) that the successively-subordinate classes, 
orders, genera, and species, into which zoologists and botan- 
ists segregate animals and plants, have not, in reaUty, 
those definite values conventionally given to them. There are 
well-marked species, and species so imperfectly defined that 
certain systematists regard them as varieties. Between 
genera, strong contrasts exist in many cases ; and in other 
cases, contrasts so much less decided as to leave it doubtful 
whether they constitute generic distinctions. So, too, is it 
with orders and classes : in some of which there have been 
introduced intermediate sub-divisions, having no equivalents 
in others. Even of the sub-kingdoms the same truth holds. 
The contrast between the Molliiscoida and the Mollusca, is far 
less than that between the Mollusca and the Annuloaa ; and 
there are naturalists who thiak that the Vertebrata are so 
much more widely separated from the other sub-kingdoms, 
than these are from one another, that the Fertehrata should 
have a classificatory value equal to that of all the other sub- 
kingdoms taken together. 

Now just this same indefiniteness of value, or incomplete- 
ness of equivalence, is observable in those simple and com- 
pound and re-compound groups, which we see arising by 
evolution. In every case, the endeavour to arrange the 
divergent products of evolution, is met by a difficulty like 
that which woidd n^eet the endeavour to classify the 
branches of a tree, into branches of the first, second, third, 
fourth, &c., orders — ^the difficulty, namely, that branches of 
intermediate degrees of composition exist. The illustration 
. furnished by languages wiU serve us once more. Some dia- 
lects of English are but Httle contrasted ; others are strongly 
contrasted. The alliances of the several Scandinavian tongues 
with one another are different in degree. Dutch is much. 


less distinct from German than Swedish is ; while between 
the Danish and Swedish there is so close a kinship, that they 
might almost be regarded as widely-divergent dialects. 
Similarly on comparing the larger divisions, we see that 
the various languages of the Aryan stock, have deviated 
from the original to very unlike distances. The general 
conclusion is manifest. While the kinds of human speech 
fall into groups, and sub-groups, and sub-sub-groups ; yet 
the groups are not equal to one another in valuie, nor have 
the sub-groups equal values, nor the sub-sub-groups. 

If, then, the classification of organisms results in several 
orders of assemblages, such that assemblages of the same 
order are but indefinitely equivalent ; and if, where 
evolution is known to have taken place, there have arisen 
assemblages between which the eqiiivalence is similarly in- 
definite ; there is additional reason for inferring that 
organisms are products of evolution. 

§ 126. A fact of much significance remains. If groups 
of organic forms have arisen by divergence and re-diver- 
gence; and if, while the groups have been developing 
from simple groups into compound groups, each group and 
sub-group has been giving origin to more complex forms 
of its own type ; then it is inferable that there once ex- 
isted greater structural likenesses between the members of 
allied groups, than exist now. Hence, if we take the 
simplest members of any group to be those which have 
undergone the least change ; we may expect to find a greater 
likeness between them and the simplest members of an allied 
group, than we find between the more complex members 
of the two groups. This, speaking generally, proves to 
be so. 

Between the sub-kingdoms, the gaps are extremely wide ; 
but such distant kinships as may be discerned, bear out an- 
ticipation. Speaking of that extremely-degraded vertebrate 
animal the Amphioxus, which has several molluscous traits 


in its organization, Dr Carpenter remarks, that it " furnishes 
an apt illustration of another important fact, that it is by 
the loitest rather than by the highest forms of two natural 
groups, that they are brought into closest relation." What 
are the faint traces of community between the Annuhaa and 
the Mollusca? They are the thread-cells which some of 
their inferior groups have in common with the Gcelenterata, 
More decided approximations exist between the lower 
members of classes. In tracing down the Crustacea and 
the Arachnida from their more complex to their simpler 
forms, zoologists meet with difficulties : respecting some of 
these simpler forms, it becomes a question which class they 
belong to. The Lepidodren, about which there have been 
disputes whether it is a fish or an amphibian, is inferior in the 
organization of its skeleton, to the great majority of both 
fishes and amphibia. Widely as they differ from them, the 
lower mammals have some characters in common with birds, 
which the higher mammals do not possess. 

Now since this kind of relationship of groups is not ac- 
counted for by any other hypothesis, while the hypothesis of 
evolution gives us a clue to it ; we must include it among the 
evidences of this hypothesis, which the facts of classification 

§ 127. What shall we say of these several leading truths 
when taken together P That naturalists have been gradually 
compelled to arrange organisms in groups within groups; 
and that this is the arrangement which we see arises by 
descent, alike in individual families and among races of men, 
is a striking circumstance. That while the smallest groups 
are the most nearly related, there exist beween the great 
sub-kingdoms, structural contrasts of the profoundest kind ; 
cannot but impress us as remarkable, when we see that where 
it is known to take place, evolution actually produces these 
feebly-distinguished small groups, and these strongly-dis- 
tinguished great groups. The impression made by these two 


parallelisms, which add meaning to each other, is deepened 
by the third parallelism, which enforces the meaning of both 
— the parallelism, namely, that as, between the species, 
genera, orders, classes, &c., which naturalists have formed, 
there are transitional gradations; so between the groups, 
sub-groups, and sub-sub-groups, which we know to have 
been evolved, groups of intermediate values exist. And 
these three correspondences between the known results of 
evolution, and the results here ascribed to evolution, have 
further weight given to them by the circumstance, that the 
kinship of groups through their lowest members, is just the 
kinship which the hypothesis of evolution impUes. 

Even in the absence of these specific agreements, the broad 
fact of unity amid multiformity, which organisms so strik- 
ingly display, is strongly suggestive of evolution. Freeing 
ourselves from pre-conceptions, we shall see good reason to 
think with Mr Darwin, " that propinquity of descent — the 
only known cause of the similarity of organic beings — ^is the 
bond, hidden as it is by various degrees of modification, which 
is partly revealed to us by our classifications." When we 
consider that this only known cause of similarity, joined with 
the only known cause of divergence, which we have in the 
influence of conditions, gives us a key to these likenesses 
obscured by uinlikenesses, to which no consistent interpreta- 
tion can otherwise be given, even if purely hypothetical 
causes be admitted; we shall see that were there none of 
those very remarkable harmonies above pointed out, the 
truths of classiflcation would stiU yield strong support to our 



§ 128. There was briefly set forth in § 62, a remarkable 
induction established by Von Baer ; who " found that in its 
earliest stage, every organism has the greatest number of 
characters in common with all other organisms in their 
earliest stages ; that at a stage somewhat later, its structure 
is like the structures displayed at corresponding phases by a 
less extensive multitude of organisms ; that at each subse- 
quent stage, traits are acquired which successively distin- 
guish the developing embryo from groups of embryos that it 
previously resembled — ^thus step by step diminishing the 
class of embryos which it still resembles ; and that thus the 
class of similar forms is finally narrowed to the species of 
which it is a member/' Though this generalization is to be 
taken with qualifications, yet, as an average truth, it may 
be regarded as beyond question ; and as an average truth, it 
has a profound significance. 

For if we follow out in thought the implications 
of this truth — if we conceive the germs of all kinds 
of organisms simultaneously developing; if after taking 
their first step together, we imagine at the second step, one 
half of the vast multitude diverging from the other half; if, 
at the next step, we mentally watch each of these great 
assemblages beginning to take two or more routes of 
development; if we represent to ourselves this bifurcation 
simultaneously going on, stage after stage, in all the 


branches ; we shall see that there must result an aggregate 
analogous, in its arrangement of parts, to a tree. If this vast 
genealogical tree be contemplated as a whole, made up of 
trunk, great branches, secondary branches, and so on, as hr 
as the terminal twigs ; it will be perceived that all the 
various kinds of organisms represented by these terminal 
twigs, forming the periphery of the tree, will stand related to 
each other in small groups, which are united into groups of 
groups, and so on. The embryological tree, expressing the 
developmental relations of organisms, will be similar to the 
tree which symbolizes their classificatory relations. That 
subordination of classes, orders, genera, anwi species, to which 
naturalists have been gradually led, is just that subordination 
which results from the divergence and re-divergence of 
embryos, as they all unfold. On the hypothesis of evolution, 
this paralleKsm has a meaning — vindicates that primordial 
kinship of all organisms, and that progressive differentiation 
of them, which the hypothesis alleges. But on any other 
hypothesis the parallelism is meaningless : or rather, it 
raises a difficulty ; since it implies either an effect without a 
cause, or a design without a purpose. 

§ 129. It was said above, that this great embryological 
law is to be taken with certain qualifications. The resem- 
blances which hold together great groups of embryos in their 
early stages, and which hold together smaller and smaller 
groups in their later and later stages, are not special or 
exact, but general or approximate ; and in some cases, the 
conformity to this general law is very imperfect. These 
irregularities, however, instead of being at variance with the 
hypothesis of evolution, afford further support to it. 

Observe, first, that the only two other possible suppositions 
respecting developmental changes, are negatived, the one by 
this general law and the other by the minor nonconformities 
to it. If it be said that the conditions of the case necessi- 
tated the derivation of all organisms from simple germs, and 


therefore necessitated a morphological miity in their primitive 
states ; there arises the obyious answer, that the morphologi- 
cal unity thus implied, is not the only morphological unity 
to be accounted for. Were this the only imity, the various 
kinds of organisms, setting out from a common primordial 
form, should all begin from the first to diverge individually, 
as so many radii from a centre ; which they do not. If, other- 
wise, it be said that organisms were framed upon certain 
lypes, and that those of the same type continue developing 
together in the same direction, imtil it is time for them to 
begin putting on their specialities of structure ; then, the 
answer is, that when they do finally diverge, they ought 
severally to develop in direct lines towards their final forms. 
No reason can be assigned why, having once parted company, 
some should progress towards their final forms by irreg^ular 
or circuitous routes. On the hypothesis of design, such de- 
viations are inexplicable. 

The hypothesis of evolution, however, while it pre-supposes 
those general relations among embryos which are found to 
exist, also affords explanations of these minor nonconformities. 
If, as any rational theory of evolution pre-supposes, the pro- 
gressive differentiations of organic forms from one another 
during past times, have resulted, as they are resulting stiU, 
from the direct and indirect effects of external conditions — 
if organisms have become different, either by inujiediate* 
adaptations to imlike habits of life, or by the mediate adapta- 
tions residting from preservation of the individuals most 
fitted for such habits of life, or by both ; and if the embryonic 
changes are related to the changes that were undergone by 
ancestral races ; then these irregularities must be expected. 
For the successive changes in modes of life pursued by 
successive ancestral races, can have had no regularity of 
sequence. In some cases they must have been more numerous 
than in others ; in some cases they must have been greater 
in degree than in others ; in some cases they must have been 
to lower modes, in some cases to higher modes, and in some 


cases to modes neither higlier nor lower. Of two connate races 
which diverged in the remote past, the one may have had 
descendants that have remained tolerably constant in their 
habits, while the other may have had descendants that have 
passed through widely-aberrant modes of life ; and yet some 
of these last may have eventually taken to modes of life like 
those of the divergent races derived from the same stock. 
And if the metamorphoses of embryos, indicate, in a general 
way, the changes of structure undergone by ancestors ; then, 
the later embryologic changes of such two allied races, will 
be somewhat different, though they may end in very similar 
forms. An illustration will make this clear. Mr Darwin 
says : — " Petrels are4he most aerial and oceanic of birds, but 
in the quiet sounds of Tierra del Fuego, the Puffinuria 
berardiy in its general habits, in its astonishing power of 
diving, its manner of swimming, and of flying when im- 
willingly it takes flight, would be mistaken by any one for 
an auk or grebe ; nevertheless, it is essentially a petrel, but 
with many parts of its organization profoundly modified." 
Now if we suppose these grebe-like habits to be continued 
through a long epoch, the petrel-form to be still more ob- 
scured, and the approximation to the grebe-form still closer ; 
it is manifest that while the chicks of the grebe and the 
Puffinuria will, during their early stages of development, 
display that likeness involved by their common derivation 
from some early type of bird, the chick of the Puffinuria 
will eventually begin to show deviations, representative of 
the ancestral petrel-structure, and will afterwards begin to 
lose these distinctions, and assume the grebe-structure. 

Hence, remembering the perpetual intrusions of organisms 
on one another's modes of life, often widely different ; and 
remembering that these intrusions have been going on from 
the beginning ; we shall be prepared to find that the general 
law of embryologic parallelism, is qualified by irregularities 
that are mostly small, in many cases considerable, and 


occasionally great. The hypothesis of evolution accounts for 
these : it does more — ^it implies the necessity of them. 

§ 130. The substitutions of organs and the suppressions 
of organs, are among those secondary embryological phe- 
nomena which harmonize with the belief in evolution 
but cannot be reconciled with any other belief. There are 
cases where, during its earlier stages of development, an 
embryo possesses organs that afterwards dwindle away, as 
there arise other organs to discharge the same functions. 
And there are cases where organs make their appearance, 
grow to certain points, have no functions to discharge, and 
disappear by absorption. 

We have a remarkable instance of this substitution in the 
successive temporary appliances for aerating the blood, 
which the mammalian embryo exhibits. During the first 
phase of its development, the mammalian embryo circulates 
its blood through a system of vessels distributed over what 
is called the area vasculosa — a system of vessels homologous 
with one which, among fishes, serves for aerating the blood 
until the permanent respiratory organs come into play. 
After a time, there buds out from the mammalian embryo, a 
vascular membrane called the allantois, homologous with 
one which, in birds and reptiles, replaces the first as a 
breathing apparatus. But while in the higher oviparous 
vertebrates, the aUantois serves the purpose of a lung during 
the rest of embryonic life, it does not do so in the mamma- 
lian embryo. In implacental mammals, it aborts, having no 
function to discharge; and in the higher mammals, it 
becomes " placentiferous, and serves as the means of inter- 
communication between the parent and the offspring " — ^be- 
comes an organ of nutrition more than of respiration. Now 
since the first system of external blood-vessels, not being in 
contact with a directly-oxygenated medium, cannot be very 
serviceable to the mammalian embryo as a lung ; and since 



the second system of external blood-vessels is, to the im** 
placental embryo, of no greater avail than the first ; and 
since the communication between the embryo and the 
placenta among placental mammals, might as well or better 
have been made directly, instead of by metamorphosis of 
the allantois; these substitutions appear unaccountable as 
results of design. But they are quite congruous with the 
supposition, that the mammalian type arose out of lower 
vertebrate types. For in such case, the mammalian embryo, 
passing through states representing, more or less distinctly, 
those which its remote ancestors had in common with the 
lower Fertebrata, develops these subsidiary organs in like 
ways with the lower Fertebrata. 

Even more striking than the substitutions of organs are 
the suppressions of organs. Mr Darwin names some cases 
as " extremely curious ; for instance, the presence of teeth 
in foDtal whales, which when grown up have not a tooth in 
their heads; * * * It has even been stated on good 
authority that rudiments of teeth can be detected in the 
beaks of certain embryonic birds." Not even temporary 
functions can be assigned for these organs that are first 
built up and then pulled down again. They are absolutely 
useless — their formation is absolutely superfluous. Irrecon- 
cilable with any teleological theory, they do not even har- 
monize with the theory of fixed types which are maintained 
by the development of all the typical parts, even where not 
wanted; seeing that the disappearance of these incipient 
organs during foetal life, spoils the typical resemblance. 
But while to all other hypotheses these facts are stumblings 
blocks, they yield strong support to the hypothesis of evolu- 

Allied to these cases, are the cases of what has been called 
retrograde development. Many parai^itic creatures and 
creatures which, after leading active lives for a time, eventu- 
ally become fixed, lose, in their adult states, the limbs and 
senses which they had when young. It may be allegei 


however, that these creatures could not secure the habitats 
needfiil for them, without possessing during their larval 
stages, eyes and swimming appendages which eventually 
become useless ; that though, by losing these, their organiza- 
tion retrogresses in one direction, it progresses in another 
direction ; and that, therefore, they do not exhibit the need- 
less development of a higher type on the way to a lower 
type. Nevertheless there are instances of a descent in 
organization, following an apparently-superfluous ascent. 
Mr Darwin says that in some genera of cirripedes, '" the 
larvae become developed either into hermaphrodites having 
the ordinary structure, or into what I have called comple- 
mental males, and in the latter, the development has 
assuredly been retrograde ; for the male is a mere sack, which 
lives for a short time, and is destitute of mouth, stomach, 
or other organ of importance, excepting for reproduc- 

§ 131. Comparative embryology shows us that besides 
substitutions of organs, there are what may be called substi- 
tuted modes of development. The same kind of structure 
is not always produced in the same way; and some allied 
groups of organisms have modes of evolution which appear 
to be radically contrasted. The two modes are broadly dis- 
tinguishable as the direct and the indirect They may 
severally characterize the general course of evolution as a 
whple, and the course of evolution in particular organs. 

Thus in the immense majority of articulate animals, 
metamorphoses, more or less marked and more or less 
numerous, are passed through on the way to maturity. The 
familiar transformations of insects show us how circuitous is 
the route by which the embryo-form arrives at the adult form, 
among some divisions of the Articulata. But there are 
other divisions, as the lower Arachnida, in which the unfold- 
ing of the egg into the adult takes place in the simplest 

manner : the substance grows towards its appointed shape 



by the shortest route. The Mollusca furnish contrasts which, 
though less marked, are essentially of the same nature. Among 
some Gasteropods, according to Vogt, the germ-mass, after 
undergoing its earliest changes in the same way as germ* 
masses in general, begins to transform itself bodily into the 
finished structure : in one part, the component cells coalesce 
to form the heart, in another part to form the liver, and so 
on. But in other classes of molluscs, as the Cephalopods, 
the embryo is moulded out of the blastoderm, or superficial 
layer of the germ-mass ; and the various organs, mostly aris- 
ing out of this blastoderm by a process of budding, reach 
their ultimate shapes through successive modifications, wjiile 
they grow at the expense of the nutriment absorbed from 
the rest of the germ- mass. And this indirect development 
is imi^ersal among the Fertebrata, 

Now on contemplating in their ensemble, the teicts thus 
briefly indicated, we may trace among these irregularities 
something like a general rule. The indirect development 
characterizes the most-highly-organized forms. In the 
sub-kingdom Feriebrata, which, considered as a whole, stands 
far above the rest in complexity, the development is uniformly 
indirect. It is indirect in the great mass of the Articulata, 
It is indirect in the highest Mollusca, Conversely, it is direct 
in a large proportion of the lower types. The eggs of 
Protozoa, of Coelenterata, of inferior Annuloida, originate the 
respective structures proper to them, by transformations that 
are ahnost immediate ; each of the cycle of forms passed 
through, is assumed, when the proper time comes, in the 
simplest way; and where they multiply by budding, the 
substance of the bud passes by as short a process as may be, 
into the finished form. Where among the simpler types of 
animals, the evolution is indirect, its indirectness generally 
appears to be related to some transitional mode of life, which 
the larva passes through on its way to maturity ; and where 
we find direct evolution among the more complex iypes, it is 


in their most degraded members : instance the Acari among 
the Articulata.* 

We have before found that the facts of social organization, 
furnish us with hints towards interpreting the phenomena 
exhibited in individual organisms. Let us see whether 
analogies hence derived, do not help us here. A factory, or 
other producing establishment, or a town made up of such 
establishments, is an agency for elaborating some commodity 
consumed by society at large ; and may be regarded as 
analogous to a gland or viscus in an individual organism. If, 
now, we inquire what is the primitive mode in which one of 
these producing establishments grows up, we find it to be 
this. A single worker, who himself sells the produce of his 
labour, is the germ. His business increasing, he employs 
helpers — ^his sons or others ; and having done this, he be- 
comes a vendor not only of his own handiwork, but of that 
of others. A further increase of his business compels him to 
multiply his assistants, and his sale grows so rapid that he is 
obliged to confine himself to the process of selling ; that is, 
he ceases to be a producer, and becomes simply a channel 
through which the produce of others is conveyed to the 
public. Should his prosperity rise yet higher, he finds that 
he is unable to manage even the sale of his commodities, and 
has to employ others, probably of his own family, to aid him 
in selling ; that is, to him as a main channel are now added 
subordinate channels ; and so on continuously. Moreover, 

* It may be urged that the mode of development is obviously related to the 
aise of the mass which is to be transformed into the embryo. Doubtless it is 
true that direct transformation is characteristic of small ova, and indirect trans- 
formation of large ova ; and some such connexion may be necessary. Very pos- 
sibly that polarity of the physiological units, which determines the specific structure, 
will not act throughout a large mass in such way as to transform it bodily into 
the specific structure ; though it will thus act throughout a small mass. But that 
the bulk of the ovum is not the iole cause of this diflference of method, is proved 
by the fact that in some cases where the development is comparatively direct, as 
in Aeteotif the ovum is very much larger than in cases where it is comparatively 
indirect, as in minute insects. 


when there grow up in one place> as a Manchester or a 
Birmingham, many establishments of like kind, this process 
is carried still further. There arise factors and agents, who 
are the channels through which are transmitted the pro- 
duce of many mills ; and we believe that primarily, these 
factors were manufacturers who undertook to dispose of the 
produce of smaller houses as well as their own, and ultimately 
became salesmen only. Now this, which is the original 
mode in which social agencies of all kinds are evolved, 
does not continue to be the mode. There is a tendency 
everywhere manifested to substitute a direct process for this 
indirect process. Manufacturing establishments are no 
longer commonly developed through the series of modifica- 
tions above described ; but mostly arise by the immediate 
transformation of a number of persons into master, clerks, 
foremen, workers, &c. Instead of business-partnerships 
being formed, as they originally were, by some slow unob- 
trusive union between traders and their sons or assistants ; 
we now have joint-stock-companies resulting by sudden 
metamorphoses of groups of citizens. The like is true with 
larger and more complex social agencies. A new town in 
the United States arises not at all after the old method of 
gradual accimiulations round a nucleus, and successive small 
modifications of structure accompanying increase of size; 
but it grows up over a large area, according to a pre-deter- 
mined plan ; and there are developed at the outset, those 
various civil, ecclesiastical, and industrial centres, which the 
incipient city will require. Even in the formation of 
colonies we may similarly see, that the whole type of social 
organization proper to the race from which the colony comes, 
begins at once to show itself. There is not a gradual passing 
through all those developmental phases passed through by 
the mother-society; but there is a comparatively direct 
transformation of the assemblage of colonists, into a social 
organism allied in structure to the social organism of which 
it was an ofiset. 


Let UB now return to the development of individual 
organisms; carrying back this idea with us. On the 
hypothesis of evolution, all organs must have been originally 
formed after the indirect method, by the accumulation of 
modifications upon modifications; and if the development of 
the embryo repeats the development of ancestral races, 
organs must be thus formed in the embryo. To a consider- 
able .extent they are thus formed. There is a striking 
parallelism between the mode in which, as above described, 
manufacturing agencies are originally evolved, and the 
mode in which secreting organs are evolved. Out of the 
group of bile-cells forming the germ of the liver, some 
centrally-placed ones, lying next to the intestine, are trans- 
formed into ducts through which the secretion of the peri- 
pheral bile-cells is poured into the intestine ; and as the peri- 
pheral bile-cells multiply, there similarly arise secondary 
ducts emptjdng themselves into the main ones ; tertiary ones 
into these; and so on. But while in this and in other 
organs, the development remains in a great degree indirect ; 
there are organs, as the heart, in which it is comparatively 
direct. The heart of the vertebrate embryo does not arise 
from a bud ; but it is first traceable as an aggregated mass 
of cells, becoming distinct from the cells amid which it is 
imbedded : its transformation into a contractile chamber, is 
effected by the consolidation of its outer cells while its inner 
cells liquify. And the comparatively direct development 
thus displayed in some organs of the higher embryos, is, as 
we have seen, characteristic of the entire development in 
many lower embryos. 

On the hypothesis of evolution, the direct mode of de- 
velopment in animals, must have been substituted for the 
indirect mode ; as we see that it is substituted in societies. 
How comes it to have been substituted P By studying the 
cause of the substitution in the social organism, we may 
perhaps get some insight into its cause in the individual or- 
ganism. The direct mode of forming social agencies 


replaces tlie indirect mode, wlien these social agencies have 
either been so long established, or have become so prevalent, or 
both, as to modify the people's habits and ideas. Groups 
of citizens unite into corporate bodies which quickly organ- 
ize, because the habit of forming such combinations has so 
far modified the thoughts and feelings of citizens, that it 
becomes natural to them thus to arrange themselves. So, 
too, is it with the men who form a colony. The rapid as- 
sumption by them of a social structure, as similar as circum- 
stances permit to the structure of the mother-society, is 
manifestly due to the fact, that the organization of the 
mother-society has moulded the emotions and beliefs of its 
members into conformity with itself; so that when some of 
its members are transferred to a colony, they arrange 
themselves directly into a structure of like type with that 
of the mother-society : they do not repeat all the stages 
through which the mother-society passed, because their 
natures have been too far modified to allow of their doing 
this. That action and reaction between a social 

organism and its imits, which we here see accounts for 
changes in modes of social development, must be paralleled 
by the action and reaction between an individual organism 
and its imits. Various classes of phenomena compelled 
us to conclude, that each kind of organism is composed of 
physiological units, having certain pecuUarites which force 
them to arrange themselves into the form of the species to 
which they are peculiar. And in the chapters on Genesis, 
Heredity, and Variation, we saw reason to believe, that 
while the polarities of the physiological imits determine the 
structure of the organism as a whole; the organism as a 
whole, if its structure is changed by incident forces, reacts 
on the physiological units, and modifies them towards con- 
formity with its new structure. Now this action and reac- 
tion between an organic aggregate and its imits, tending 
ever to bring the two into absolute harmony, must be con- 
tinually making the developmental processes more direct; 


and will show its effects in all kinds of ways and degrees, 
according to the ancestral history of each species. Suppos- 
ing it were possible for a race of organisms to have con- 
tinued propagating itself through an indefinitely-long 
period without any change of conditions, necessitating 
change of structure ; there would be reached so complete a 
congruity between the organic aggregate and its physiologi- 
cal units, that the units would arrange themselves directly 
into a structure like that of the adult organism : the germ 
would put on the proper characters of the species, with little 
or no transposition of substance. But in the absence of 
any such constancy of conditions and structure, what may wo 
expect? We may expect that where the conditions and 
structure have been most constant, the mode of develop- 
ment will be the most direct ; and that it will be the most 
indirect, where there have been the greatest and most 
numerous changes in the habits and structures of ancestral 
races of organisms. And we may also expect that develop- 
mental changes corresponding to early ancestral forms, will 
undergo an obliteration that is great in proportion to the 
fixity of organization that has been since maintained. The 
facts appear in harmony with this conclusion. We see a 
comparatively-direct development in those inferior types of 
animals, which show us, by their inferiority, that they have 
not, since the commencement of organic life, passed through 
many sets of changes. And where we find direct de- 
velopment among higher types of animals, it characterizes 
the simpler rather than the more complex members of the 

Between different parts in the same embryo, there are un- 
likenesses in the method of formation, which seem to have 
kindred meanings. The heart, of which the development is 
in great measure direct, is an organ that appears compara- 
tively early among the ascending grades of organic forms ; 
and having appeared, retains throughout the character of a 
hollow muscle. Conversely, the organs which develop with 


great indirectnefls, are the organs of external relation; 
which, in the progrefls of orgaiuc forms, undergo various 
metamorphoses. Some light, too, is thus thrown on 

certain irregularities in the order of development of organs. 
If we contemplate those continuous actions and reactions 
which tend ever to establish a balance betwe^i an organic 
aggregate and its units ; we shall see that the effect which 
the units composing any organ, produce on the organism as a 
whole, will depend, partly on the permanence of such organ, 
and partly on its proportional mass. The influence of any 
force, is a product of its amount multiplied into the Hme during 
which it has acted. Hence, a larger part of the aggregate 
acting for a shorter time, will impress itself on the phy- 
siological units, as much as a smaller part acting for a 
longer time ; and may thus begin to show its influence in 
the developmental changes, as soon as, or even earlier than, a 
part that has existed for a greater period. Thus it becomes 
comprehensible why, in certain Entozoa which have im- 
mensely-developed generative systems, the rudiments of the 
generative systems are the first to become visible. And 
thus are also explicable, anomalies such as those pointed 
out by Prof. Agassiz — the appearance, in some cases, of 
traits characterizing the species, at an earlier period of 
development than traits characterizing the genus. 

. § 132. So that while the embryologic law enunciated by 
Von Baer, is in harmony with the hypothesis of evolution, 
and is, indeed, a law which this hypothesis implies; the 
minor nonconformities to the law, are also interpretable by 
this hypothesis. Parallelism between the courses of develop- 
ment in species that had a common ancestry, is liable to be 
variously modified in correspondence with the later ancestral 
forms passed through after divergence of such species. The 
substitution of a direct for an indirect process of formation, 
which we have reason to believe will show itself, both in the 
unfolding of the entire organism and in the unfolding of par- 


ticular organs, must obscure the embryologic history. And 
the parts influencing the whole in degrees varying with their 
masses, there results a further influence which, from the out- 
set, must begin to modify the metamorphoses of each kind of 
embryo ; and cause it to show incipient divergences from 
embryos which had ancestral histories the same as its own. 
Thus we find three different causes conspiring in endless 
ways and degrees, to produce deviations from the general law 
—causes which are manifestly capable of producing, under 
special conditions, changes in apparent contradiction to this 



§ 133. Leaviho oat of oonaideratioii the paraUelisiii of 
development which characterizes organianiB belonging to each 
gnmp, that community of plan which exists among them 
when they are mature, is extremely remarkable and extremely 
snggestive. As before shown (§ 103), neither the supposition 
that these combinations of attributes which unite classes are 
fortuitous, nor the supposition that no other combinations 
were practicable, nor the supposition of adherence to pre- 
determined typical plans, suffices to explain the £Eu;ts. An 
instance will best prepare the reader for seeing the true 
meaning of these fundamental likenesses. 

Under the immensely-Taried forms of insects, greatly elon- 
gated like the dragon-fly, or contracted in shape like the 
lady-bird, winged like the butterfly, or wingless like the 
flea, we find this character in common — ^there are primarily 
twenty segments. These segments may be distinctly marked, 
or they may be so fused as to make it difficult to find the 
divisions between them. This is not all. It has been 
shown that the same number of segments is possessed by all 
the Crustacea* The highly-consolidated crab, and the squiUa 
with its long, loosely-jointed divisions, are composed of the 
same number of somites. Though, in the higher crustaceans, 
some of these successive indurated rings, forming the exo- 
skeleton, are never more than partially marked off from each 


other; yet they are indentifiable as homologous with 
segmentSj which, in other crustaceans, are definitely 
divided. What, now, can be the meaning of this 

community of structure among these hundreds of thousands of 
species filling the air, burrowing in the earth, swimming in 
the water, creeping about among the sea- weed, and haying 
such enormous dLSerences of size, outline, and substance, as 
that no community would be suspected between them P Why 
under the down-covered body of the moth and imder the 
hard wing-cases of the beetle, should there be discovered the 
same number of divisions as in the calcareous framework of 
the lobster P It cannot be by chcmce that there exist just 
twenty segments in all these hundreds of thousands of species. 
There is no reason to think it was necessary, in the sense 
that no other number would have made a possible organism. 
And to say that it is the result of desigvr— to say that the Cre* 
ator followed this pattern throughout, merely for the purpose 
of maintaining the pattern — ^is to assign a motive which, if 
avowed by a human being, we should call whimsical. No 
rational interpretation of this and hosts of like morphological 
truths, can be given except by the hypothesis of evolution ; 
and from the hypothesis of evolution they are corollaries. 
If organic forms have arisen from common stocks by per- 
petual divergences and redivergences — ^if they have continued 
to inherit, more or less clearly, the characters of ancestral 
races; then there will naturally result these conummities of 
fundamental structure among extensive assemblages of crea- 
tures, that have severally become modified in countless ways 
and degrees, in adaptation to their respective modes of 
life. To this let it be added, that while the belief 

in an intentional adhesion to a pre-determined pattern 
throughout a whole group, is totally negatived by the occur- 
rence of occasional deviations from the pattern ; such devi- 
ations are reconcilable with the belief in evolution. As 
pointed out in the last chapter, there is reason to think that 
remote ancestral traits, will be obscured more or less according 


as the superpooed modifications of stmctare, liave or have 
not been great or long maintainecL Hence, thongli the occur- 
rence of articulate animals, such as spiders and mites, having 
fewer than twenty segments, is £a,tal to the supposition that 
twenty segments was decided on for the three groups of 
superiOT Ariiculaia; it is not incongruous with the supposition, 
that some primitiTe race of articulate animals, bequeathed to 
these three groups this common typical character — a character 
which has nevertheless, in many cases, become greatly ob- 
scured, and in some of the most aberrant orders of these 
classes, quite lost. 

I 134. Besides these wide-embracing and often deeply- 
hidden homologies, which hold together different animals^ 
there are the scarcely-less significant homologies between 
different organs of the same animal. These homologies^ 
like the others, are obstacles to the supernatural interpreta- 
tions, and supports of the natural interpretation. 

One of the most familiar and instructive instances is 
furnished by the vertebral column. Snakes, which move 
sinuously through and over plants and stones, obviously 
need a segmentation of the bony axis from end to end ; and 
inasmuch as flexibility is required throughout the whole 
length of the body, there is advantage in the comparative 
imiformity of this segmentation : the creature's movements 
would be impeded if, instead of a chain of vertebrae varying 
but little in their lengths, there existed in the middle of the 
series some long bony mass that would not bend. But in most 
of the higher Fertebrata, the mechanical actions and reac- 
tions demand that while some parts of the vertebral axis shall 
be flexible, other parts shall be inflexible. Inflexibility is 
especially requisite in that part of the vertebral column 
called the sacrum ; which, in mammals and birds, forms a 
ftilcnun exposed to the greatest strains which the skeleton 
has to bear. Now in both mammals and birds, this rigid 
portion of the vertebral column is not made of one long 


segment or vertebra^ but of sev^eral Begments fused to- 
gether* In man there are five of these confluent sacral 
vertebrse ; and in the ostrich tribe they number from seven- 
teen to twenty. Why is this P Why, if the skeleton of 
each species was separately contrived, was this bony mass 
made by soldering together a number of vertebraD like those 
forming the rest of the column, instead of being made out of 
one simple piece f And why, if typical uniformity was to be 
maintained, does the number of sacral vertebrae vary within 
the same order of birds ? Why, too, should the develop- 
ment of the sacrum be by the round-about process of first 
forming its separate constituent vertebreo, and then de- 
stroying their separateness P In the embryo of a mammal 
or bird, the substance of the vertebral column is, at the out- 
set, continuous. The segments that are to become vertebreo, 
arise gradually in the midst of this originally-homogeneous 
axis. Equally in those parts of the spine which are to 
remain flexible, and in those parts which are to grow 
rigid, these segments are formed ; and that part of the spine 
which is to compose the sacrum, having passed out of its ori- 
ginal unity into disunity, by separating itself into segments, 
passes again into unity by the coalescence of these segments. 
To what end is this construction and re-construction P If, 
originally, the spine in vertebrate animals consisted from 
head to tail of separate moveable segments, as it does still in 
fishes and some reptiles — ^if, in the evolution of the higher 
rertebrata, certain of these moveable segments were ren- 
dered less moveable with respect to each other, by the 
mechanical conditions to which they are exposed, and at 
length became relatively immoveable ; it is comprehensible 
why the sacrum formed out of them, should continue ever 
after to show more or less clearly its originally-segmented 
structure. But on any other hypothesis, this segmented 
structure is inexplicable. ** We see the same law in 

comparing the wonderfully complex jaws and legs in crusta- 
ceans," says Mr Darwin : referring to the well-known fact 


that those nmnerons lateral appendages which, in the lower 
crustaceans most of them serve as legs, and have like shapes, 
are, in the higher crostaoeans, some of them represented by 
enoim^onsly-deYeloped daws, and others by Tariotisly-modi- 
fied foot-jaws. *'It is familiar to aknost every one," he 
continues, '^that in a flower the relative position of the 
sepals, petals, stamens, and pistils, as well as their intimate 
structure, are intelligible on the view that they consist of 
metamorphosed leaves arranged in a spire. In monstrous 
plants we often get direct evidence of the possibility of one 
organ being transformed into another ; and we can actually 
see in embryonic crustaceans and in many other animals, and 
in flowers, that organs, which when mature become extremely 
different, are at an early stage of growth exactly aUke." 
♦ ♦ ♦ "Why should one crustacean, which has an ex- 
tremely complex mouth formed of many parts, consequently 
always have fewer legs ; or conversely, those with many legs 
have simpler mouths? Why should the sepals, petals, 
stamens, and pistils in any individual flower, though fitted 
for such widely-different purposes, be all constructed on the 
same pattern P " 

To these and countless similar questions, the theory of 
evolution furnishes the only rational answer. In the course 
of that change from homogeneity to heterogeneity of struc- 
ture, displayed in evolution under every form, it will neces- 
sarily happen that from organisms made up of numerous 
like parts, there will arise organisms made up of parts more 
and more unlike : which unlike parts wiU nevertheless con- 
tinue to bear traces of their primitive likeness. 

§ 135. One more striking morphological fact, near akin 
to some of the facts dwelt on in the last chapter, must be 
here set down — the frequent occurrence, in adult animals 
and plants, of rudimentary and useless organs, which are 
homologous with organs that are developed and useMin 
allied animals and plants. In the last chapter we saw that 


during the development of embryos, there often arise organs 
which disappear on being replaced by other organs dis- 
charging the same functions in different ways ; and that in 
some cases, organs develop to certain points, and are then 
re-absorbed without performing any functions. But very 
generally, the partially-developed organs are retained 
throughout life. 

The osteology of the higher Fertebrata, supplies abundant 
examples. Vertebral processes which, in one tribe, are fully 
formed and ossified from independent centres, are, in other 
tribes, mere tubercles not having independent centres of 
ossification. While in the tail of this animal, the vertebrsB 
are severally composed of centrum and appendages, in the 
tail of that animal, they are simple osseous masses without 
any appendages ; and in another animal, they have lost their 
individualities by coalescence with neighbouring vertebrsQ 
into a rudimentary tail. From the structures of the limbs, 
analogous facts are cited by comparative anatomists. The 
undeveloped state of certain metacarpal bones, characterizes 
whole groups of mammals. In one case we find the normal 
number of digits ; and, in another case, a smaller nmnber 
with an atropliied digit to make out the complement. Here is 
a digit with its full number of phalanges ; and there a digit of 
which one phalange has been arrested in its growth. Still 
more remarkable are the instances of entire limbs being rudi- 
mentary ; as in certain snakes, which have hind legs hidden ' 
beneath the integument. So, too, is it with the dermal ap- 
pendages. Some of the smooth-skinned amphibia have scales 
buried in the skin. The seal, which is a mammal considerably 
modified in adaptation to an aquatic life, and which uses its 
feet mainly as paddles, has toes that still bear external nails ; 
but the manatee, which is a much more transformed mam- 
mal, has nailless paddles, which, when the skin is re- 
moved, are said, by Humboldt, to display rudimentary nails 
at the ends of the imbedded digits. Nearly all birds are 
covered with developed feathers, severally composed of a shaft 



bearing fibres, each of wbicb again bears a fringe of down. 
But in some birds, as in the ostrich, varions stages of arrested 
development of the feathers may be traced ; beginning with 
the unusually-elaborated feathers of the tail, and ending with 
those about the beak, which are reduced to simple hairs. Kor 
is this the extreme case. In the Apteryx we see the whole 
of the feathers reduced to a hair-like form. Again, the hair 
which commonly covers the body in mammals, is compara- 
tively rudimentary over the greater part of the human body, 
and is in some parts reduced to mere down— down which 
nevertheless proves itself to be homologous with the hair of 
mammals in general, by occasionally developing into the 
original form. Numerous cases of aborted organs are given 
by Mr Darwin, of which a few may be here added. " No- 
thing can be plainer," he remarks, 'Hhan that wings are formed 
for flight, yet in how many insects do we see wings so reduced 
in size as to be utterly incapable of flight, and not rarely 
lying under wing-cases, firmly soldered together?" ♦ ♦ * 
" In plants with separated sexes, the male flowers often have 
a rudrment of a pistil ; and Kolreuter found that by crossing 
such male plants with an hermaphrodite species, the rudi- 
ment of the pistil in the hybrid oflspring was much increased 
in size ; and this shows that the rudiment and the perfect pistil 
are essentially alike in nature." And then, to complete the 
proof that these undeveloped parts are marks of descent from 
races in which they were developed, there are not a few direct 
experiences of this relation. " We have plenty of cases of 
rudimentary organs in our domestic productions — as the 
stump of a tail in tailless breeds — ^the vestige of an ear in 
earless breeds — ^the re-appearance of minute dangling horns 
in hornless breeds of cattle." 

Here, as before, the teleological doctrine fails utterly; 
for these rudimentary organs are useless, and occasionally 
even detrimental. The doctrine of typical plans is equally 
out of court ; for while, in some members of a group, rudi- 
mentary organs completing the general type are traceable. 


in other members of the same group, such organs are unre- 
presented. There remains only the doctrine of evolution ; 
and to this, these rudimentary organs offer no difficulties. 
On the contrary, they are among its most striking evi- 

§ 136. The general truths of morphology thus coincide in 
their implications. Unity of type, maintained under extreme 
dissimilarities of form and mode of life, is explicable as re- 
sulting from descent with modification ; but is otherwise 
inexplicable. The likenesses disguised by unlikenesses, which 
the comparative anatomist discovers between various organs 
in the same organism, are worse than meaningless if it be 
supposed that organisms were severally framed as we now 
see them ; but they fit in quite harmoniously with the belief, 
that each kind of organism is a product of accumulated 
modifications upon modifications. And the presence in all 
kinds of animals and plants, of functionally-useless parts 
corresponding to parts that are functionally-useful in allied 
animals and plants, while it is totally incongruous with the 
belief in a construction of each organism by miraculous in- 
terposition, is just what we are led to expect by the belief 
that organisms have arisen by progression. 

25 ♦ 



§ 137. In §§ 105 and 106, we contemplated the phenomena 
of distribution in Space. The general conclusions reached, 
in great part based on the evidence brought together by Mr 
Darwin, were that, " on the one hand, we have similarly-con- 
ditioned, and sometimes nearly-adjacent, areas, occupied by 
quite different Faunas. On the other hand, we have areas 
remote from each other in latitude, and contrasted in soil as 
weU as climate, which are occupied by closely-aUied Faunas." 
Whence it was inferred that " as like organisms are not uni- 
versally, or even generally, found in like habitats ; nor very 
unUke organisms, in very unlike habitats ; there is no manifest 
pre-deiermined adaptation of the organisms to the habitats.'' 
In other words, the facts of distribution in Space, do not 
conform to the hypothesis of design. At the same 

time we saw that " the similar areas peopled by dissimilar 
forms, are those between which there are impassable barriers ; 
while the dissimilar areas peopled by similar forms, are those 
between which there are no such barriers ;" and these 
generalizations appeared to be in harmony with the abund- 
antly-illustrated truth, " that each species of organism tends 
ever to expand its sphere of existence — ^to intrude on other 
areas, other modes of life, other media." 

By way of showing still more clearly the effects of this 
competition among races of organisms, let me here add some 
recently-published instances of the usurpations of areas, and 


cliaiiges of d&tribution hence resulting. In the Natural flta- 
tary Review for January, 1864, Dr Hooker quotes as follows 
from some New Zealand naturalists : — " You would be surprised 
at the rapid spread of European and other foreign plants in 
this country. -All along the sides of the main lines of road 
through the plains, a Polygonum (avicula/re) , called ' Cow 
Grass,' grows most luxuriantly, the roots sometimes two feet 
in depth, and the plants spreading over an area from four to 
five feet in diameter. The dock (Bumex ohtusifolius or B. 
crispus) is to be found in every river bed, extending into the 
valleys of the mountain rivers, until these become mere tor- 
rents. The sow-thistle is spread all over the country, growing 
luxuriantly nearly up to 6000 feet. The water-cress increases 
in oui' still rivers to such an extent, as to threaten to choke 
them altogether : * * * I have measured stems twelve feet 
long and three-quarters of an inch in diameter. In some of 
the mountain districts, where the soil is loose, the white clover 
is completely displacing the native grasses, forming a close 
sward. * * * In fact, the young native vegetation appears 
to shrink from competition with these more vigorous in- 
truders." " The native (Maori) saying is, ' as the white 
man's rat has driven away the native rat, so the European 
fly drives away our own, and the clover kills our fern, so 
wiU the Maoris disappear before the white man himself.' " 

Given this universal tendency of the superior to over- 
run the habitats of the inferior ; let us consider what, on the 
hypothesis of evolution, will be the effect* on the geo- 
graphical relationships of species. 

§ 138. A race of organisms cannot expand its sphere of 
existence,, without subjecting itself to new external conditions. 
Those of its members which spread over adjacent areas, 
inevitably come in contact with circumstances partially 
different from their previous circumstances; and such of 
them as adopt the habits of other organisms, necessarily 
experience re-actions more or less contrasted with the re* 


actions before experienced. Now if changes of organic 
structure are caused, directly or indirectly, by changes in 
the incidence of forces ; there must result unlikenesses of 
structure between the diyisions of a race which colonizes 
new habitats. Hence, in the absence of obstacles to migra- 
tion, we may anticipate manifest kinships between the 
animals and plants of one area, and those of areas adjoining it. 
This inference corresponds with an induction before set 
down (§ 106). In addition to the illustrations of it already 
quoted from Mr Darwin, his pages fiimish others. One is 
that species which inhabit islands are habitually allied to 
species which inhabit neighbouring main lands; and an- 
other is that the faunas of clustered islands show marked 
similarities. "Thus the several islands of the Galapagos 
Archipelago are tenanted," says Mr Darwin, "in a quite 
marvellous manner, by very closely related species; so that 
the inhabitants of each separate island, though mostly dis- 
tinct, are related in an incomparably closer degree to each 
other than to the inhabitants of any other part of the world." 
Mr Wallace has traced " variation as specially influenced by 
locality " among the PapilionidcB inhabiting the East Indian 
Archipelago : showing how " the species and varieties of 
Celebes possess a striking character in the form of the 
anterior wings, different from that of the allied species and 
varieties of all the surrounding islands ; " and how " tailed 
species in India and the western islands lose their tails as 
they spread eastward through the archipelago." During 
his travels on the Upper Amazons, Mr Bates found that 
" the greater part of the species of ItJiomuB changed from 
one locality to another, not further removed than 100 to 200 
miles ; " that " many of these local species have the appear- 
ance of being geographical varieties;" and that in some 
species " most of the local varieties are connected with their 
parent form by individuals exhibiting all the shades of 

Further general relationships are to be inferred. If 


races of organisms, ever being thrust by pressure of popula- 
tion into new habitats, undergo modifications of structure as 
they diverge more and more widely in space, it follows that, 
speaking generally, the widest divergences in Space will 
indicate the longest periods during which the descendants 
from a conmion stock have been subject to modifying con- 
ditions ; and hence that, among organisms of the same 
group, the smaller constrasts of structure will be limited 
to the smaller areas. This we find: "varieties being,'* 
as Dr Hooker says in his Flora of Tasmania, " more re- 
stricted in locality than species, and these again than 
genera." Again, if races of organisms spread, and 

as they spread are altered by changing incident forces ; it 
follows that where the incident forces vary greatly within 
given areas, the alterations will be more numerous than in 
equal areas which are less- variously conditioned. This, too, 
proves to be the fact. Dr Hooker points out that the most 
imiform regions have the fewest species ; while in the most 
multiform regions the species are the most numerous. 

§ 139. Let us consider next, how the hypothesis of 
evolution corresponds with the facts of distribution, not over 
different areas, but through different media. If all forms of 
organisms have descended from some primordial simplest 
form, it follows that, since this primordial simplest form 
must have inhabited some one medium out of the several 
media which organisms now inhabit, the peopling of other 
media by its descendants, implies migration from one 
mediimi to others — ^implies adaptations to media quite unlike 
the original medium. To speak specifically — ^water being 
the medium in which the lowest living forms exist, it is 
implied that the earth and the air have been colonized from 
the water. Great difficulties appear to stand in the way of 
this assumption. Bidiculing those who contend for the uni- 
serial development of organic forms, who have, indeed, laid 
themselves open to ridicule by their many untenable pro- 


positions^ Von Baer writes — "A fish, swimming towards 
the shore, desires to take a walk, but finds his fins useless. 
They diminish in breadth for want of use, and at the same 
time elongate. This goes on with children and grandchil- 
dren for a few millions of years, and at last who can be as- 
tonished that the fins become feet P It is stiU more natural 
that the fish in the meadow, finding no water^ should gape 
after air, thereby, in a like period of time developing 
lungs; the only difficulty being that in the meanwhile, 
a few generations must manage without breathing at 
all." Though, as thus presented, the belief in a 

transition looks laughable ; and though such derivation of 
terrestrial vertebrates by direct modification of the piscine 
type, is untenable ; yet we must not therefore conclude that 
no migrations of the kind alleged can have taken place. 
The adage that " truth is stranger than fiction," applies quite 
as much to Nature in general as to human life. Besides the 
fact that there are certain fish which actually do " take a 
walk " without any very obvious reason ; and besides the 
fact that sundry fish ramble about on land when impelled 
to do so by the drying- up of the waters inhabited by them ; 
there is the still more astounding fact, that one kind of fish 
climbs trees. Few things seem more obviously impossible, 
than that a water-breathing creature without efficient limbs* 
should ascend eight or ten feet up the trunk of a palm ; and 
yet the Anahas scandens does as much. To previous testi- 
monies on this point, Capt. Mitchell has recently added 
others. Such remarkable cases of temporary changes of 
media, will prepare us for conceiving how, imder special con- 
ditions, permanent changes of media may have taken place ; 
and for considering how the doctrine of evolution is eluci- 
dated by them. 

Both marine organisms and fresh-water organisms, are 
many of them left from time to time partially or completely 
without water ; and the creatures which show the power to 
change their media temporarily or i)ermanently, are in veiy 


many cases, of the kinds most liable to be thus deserted by 
tlieir medium. Let us consider what the sea-shore shows 
us. Twice a-day the rise and the fall of the tide, 

covers and uncovers countless plants and animals, fixed and 
moving ; and through the alternation of spring and neap 
tides, it results that the exposure of the organisms living low 
down on the beach, varies both in frequency and duration : 
while some of them are left dry only once a fortnight for a 
very short time, others a little higher up, are left dry during 
two or three hours at several ebb tides every fortnight. 
Then by small gradations we come to such as, living at the 
top of the beach, are bathed by salt-water only at long in- 
tervals ; and still higher to some which are but occasionally 
splashed in stormy weather. What, now, do we find among 
the orgaaisms thus subject to various regular and irregular 
alternations of media ? Besides many plants and many fixed 
animals, we find numerous moving animals ; some of which 
are confined to the lower zones of this littoral region, but others 
of which wander over the whole of it. Omitting the humbler 
animal forms, it will suffice to observe that each of the two 
great sub-kingdoms, Mollusca and Articulatay supplies ex- 
amples of creatures having a wide excursiveness within this 
region. We have gasteropods which, when the tide is down, 
habitually creep snail-like over sand and sea- weed, even up as 
far as high- water mark. We have several kinds of crustaceans, 
of which the crab is the most conspicuous, running about on 
the wet beach, and sometimes rambling beyond the reach of 
the water. And then note the striking fact, that each of these 
forms thus habituated to changes of media, is allied to forms 
that are mainly or wholly terrestrial. On the West Coast of 
Ireland, marine gasteropods are found on the rocks three hun- 
dred feet above the sea, where they are only at long intervals 
wetted by the spray ; and though between gasteropods of this 
class and land-gasteropods the differences are considerable, yet 
the land-gasteropods are more closely allied to them than to 
any other Mollusca. Similarly, the two highest orders of 


crustaceans have their species wMcli live occasionally, or 
almost entirely, out of the water : there is a kind of lobster 
in the Mauritius which climbs trees ; and there is the land- 
crab of the West Indies, which deserts the sea when it reaches 
maturity, and re- visits it only to spawn. Seeing, thus, how 
there are many kinds of marine creatures whose habitat 
habitually exposes them to changes of media ; how some of 
the higher kinds so circumstanced, show a considerable adapt- 
ation to both media ; and how these amphibious kinds are 
allied to kinds that are mainly or wholly terrestrial ; we 
shall see that the migrations &om one medium to another, 
which evolution pre-supposes, are by no means impracticable. 
With such evidence before us, the assumption that the dis- 
tribution of the Vertehrata through media so different as air 
and water, may have been gradually effected in some analogoiis 
manner, would not be altogether unwarranted, even had we 
no clue to the process. We shall find, however, a tolerably 
distinct clue. Though rivers, and lakes, and pools, 

have no sensible tidal variations, they have their rises and 
falls, regular and irregular, moderate and extreme. Especially 
in tropical climates, we see them annually full for a certain 
number of months, and then dwindling away and drying up. 
This drying up may reach various degrees, and last for various 
periods : it may go to the extent only of producing a liquid 
mud, or it may reduce the mud to a hardened, fissured solid ; 
it may last for a day or two or for months. That is to say, 
aquatic forms which are in one place annually subject to a 
slight want of water for a short time, are elsewhere subject 
to greater wants for longer times : we have gradations of 
transition, analogous to those which the tides fiimish. Now 
it is well known that creatures inhabiting such waters, have, 
in various degrees, powers of meeting these contingences. 
The contained fish either bury themselves in the mud 
when the dry season comes, or ramble in search of other 
waters. This is proved by evidence from India, Ghiiana, Siam, 
Ceylon ; and some of these fish, as the Ariahda scandens, are 


known to survive for days out of the water. But the facts of 
greatest significance are furnished by an aUied class of 
rertebrata, aJmost pecuKar to habitats of this kind. The 
Amphibia are not, like fish, habitually found in waters that 
are never partially or wholly dried up ; but they nearly all 
inhabit waters which, at certain seasons, evaporate, in great 
measure or completely — ^waters in which most kinds of fish 
cannot exist. And what are the leading structural traits of 
these Amphibia? They have two respiratory systems — 
pulmonic and branchial — ^variously developed in different 
orders ; and they have two or four limbs, also variously de- 
veloped. Further the class Amphibia consists of two groups, 
in one of which this duality of the respiratory system is 
permanent, and the development of the limbs always incom- 
plete ; and in the other of which the branchiaB disappear as 
the lungs and limbs become fully developed. The lowest 
group, the Perennibranchiata, have organs homologous with 
the air-bladders of fishes, transformed in various degrees 
into lungs, imtil " in the 8ire7i, the puhnonic respiration is 
more extensive and important than the branchial ; ** and to 
these creatures, having a habitat partially aerial and partially 
aquatic, there are at the same time supplied, in the shallow 
water covering soft mud, the inechanical conditions which 
render swimming difficult and rudimentary limbs ubcM. 
In the higher group, the Gaducibranchiata, we find still more 
suggestive transformations. Having at first a structure re- 
sembling that which is permanent in the perennibranchiate 
amphibian, the larva of the caducibranchiate amphibian, 
pursues for a time a similar life; but eventually, the 
changes are carried further in the same direction : the respir- 
ation of air, originally supplementary to the respiration of 
water, predominates over it more and more, till it replaces it 
entirely ; and an additional pair of legs is produced. This 
having been done, the creature either becomes, like the Triton, 
one which quits the water only occasionally ; or, like the 
Frog, one which pursues a life mainly terrestrial, and returns 


to the water now and then. Finally, if we ask under what 
conditions this metamorphosis of a water-breather into an 
air-breather completes itself, the answer is — ^it completes it- 
self at the time when the shallow pools inhabited by the 
larvae, are being dried up by the smmner's sun.* 

See, then, how significant are the facts when thus brought 
together. There are particular habitats in which animals are 
subject to changes of media. In such habitats exist aTn'THRla 
having, in various degrees, the power to live in both media, 
consequent on various phases of transitional organization. 
Near akin to these animals, there are some that, after passiug 
their early lives in the water, acquire more completely the 
structures fitting them to live on land, to which they then 
migrate. Lastly, we have closely-allied creatures like the 
Surinam toad and the terrestrial salamander, which, though 
they belong by their structures to the class Amphibia, are 
not amphibious in their habits— creatures the larvae of which 
do not pass their early lives in the water, and yet go through 
these same metamorphoses ! Must we then think that the 
distribution of kindred organisms through different media, 
presents an insurmountable difficulty? On the contrary, 
with facts like these before us, the evolution-hypothesis 
supplies possible interpretations of many phenomena that are 
else unaccountable. Eealizing the way in which such changes 
of media are in some cases gradually imposed by physical 
conditions, and in other cases voluntarily commenced and 
slowly increased in the search after food ; we shall begin to 
understand how, in the course of evolution, there have arisen 

♦ While these pages are passing through the press, Dr Hooker has ohliged 
me hy pointing out, that *' plants afford many excellent examples " of analogous 
transitions. He says that among true " water plants," there are found, in the 
same species, varieties which have some leaves submerged and some floating ; 
other varieties in which they are all floating ; and other varieties in which they 
are all submerged. Further, that many plants characterized by floating leaves, 
and which have all their leaves floating when they grow in deeper water, are 
found with partly aerial leaves when they grow in shallower water ; and that 
elsewhere they occur in almost dry soil with all their leaves aerial. 


those strange obscurations of one type by the externals of 
another type. When we see land-birds occasionally feeding 
by the water-side, and then learn that one of them, the water- 
ouzel, an ''anomalous member of the strictly terrestrial 
thrush family, wholly subsists by diving — grasping the stones 
with its feet and using its wings under water " — we are en- 
abled to comprehend how, under pressure of population, 
aquatic habits may be acquired by creatures organized for 
aerial life ; and how there may eventually arise an ornithic 
type, in which the traits of the bird are very much disguised. 
Finding among mammals, some that in search of prey or 
shelter, have taken to the water in various degrees, we shall 
cease to be perplexed on discovering the mammalian structure 
hidden under a fish-like form, as it is in the Cetacea. Grant 
^hat there has ever been going on that re-distribution of 
organisms, which we see still resulting from their intrusions 
on one another's areas, media, and modes of life ; and we 
have an explanation of those multitudinous cases in which 
homologies of structure are complicated with analogies. And 
while it accounts for the occurrence in one medium of or- 
ganic types fundamentally organized for another medium, 
the doctrine of evolution accounts also for the accompany- 
ing unfitnesses. Either the seal has descended from some 
mammal which little by little became aquatic in its habits, 
in which case the structure of its hinl limbs has a mean- 
ing ; or else it was specially framed for its present habi- 
tat, in which case the structure of its hind limbs is incom- 

§ 140. The facts respecting distribution in Time, which 
have more than any others been cited both in proof and in 
disproof of evolution, are too fragmentary to be conclusive 
either way. Were the geological record complete, or did it, 
as both Uniformitarians and Progressionists have habitually 
assumed, give us traces of the earliest organic forms ; the 
evidence hence derived, for or against, would have had more 


weight than any oth«r evidence. As it is, all we can do is to 
see whether such fragmentary evidence as remains, is c(m- 
gruons with the hypothesis. 

PalaBontology has shown that there is a ^' general relation 
between lapse of time and divergence of organic forms'' 
(§ 107) ; and that ^' this divergence is comparatively slow and 
continnoufly where there is continuity in the geological forma^ 
tions, but is sudden and comparatively wide, wherever there 
occurs a great break in the succession of strata." Now this 
is obviously what we should expect. The hjrpothesis implies 
structural changes that are not sudden but graduaL Hence, 
where conformable strata indicate a continuous record, we 
may expect to find successions of forms only slightly different 
from one another ; while we may rationally look for consider- 
able contrasts between the groups of forms fossilized in adj acent 
strata, where there is evidence of a great blank in the record. 

The permanent disappearances of species, of genera, and of 
orders, which we saw to be a fact tolerably- well established, is 
also a fact for which the belief in evolution prepares us. 
If later organic forms have in all cases descended from 
earlier organic forms, and have diverged during their descent, 
both from their prototjrpes and from one another ; then it 
obviously follows, that such of them as become extinct at any 
epoch, will never re-appear at a subsequent epoch ; since 
there can never again arise a concurrence and succession of 
conditions, such as those under which each particular type 
was evolved. 

Though comparisons of ancient and modem organic forms, 
prove that many types have persisted through enormous 
periods of time, without undergoing great changes ; it was 
shown that such comparisons do not disprove the occur- 
rence in organic forms, of changes great enough to produce 
what are called different types. The result of inductive in- 
quiry we saw to be, that while a few modem higher types 
yield signs of having been developed from ancient lower 
types ; and while there are many modem types which may 


have been thus developed, though we are without evidence that 
they have been so ; yet that " any admissible hypothesis of 
progressive modification must be compatible with persistence 
without progression through indefinite periods/' Now these 
results are quite congruous with the hjrpothesis of evolution. 
As rationally interpreted, evolution must in aU cases be 
tmderstood to result, directly or indirectly, from the incidence 
of forces. If there are no changes of conditions, entailing 
organic changes, organic changes are not to be expected. 
Only in organisms which fall under conditions, in conformity 
to which there arise additional modifications answering to 
additional needs, will there be that increased heterogeneity 
which characterizes higher forms. Hence, though the facts 
of palax)ntology cannot be held to prove evolution, yet they 
are in harmony with it ; and some few of them yield it 

§ 141. One general truth respecting distribution in Time, 
is, however, profoundly significant. If, instead of contem- 
plating the relations among past forms of life taken by them- 
selves, we contemplate the relations between them and the 
forms now existing ; we find a connexion which is in perfect 
harmony with the belief in evolution, but quite irreconcil- 
able with any other belief. 

Note, first, how full of meaning is the close kinship that 
exists between the aggregate of organisms now living, 
and the aggregate of organisms which lived in the most 
recent geologic times. In the last-formed strata, nearly aU 
the imbedded remains are those of species which still flourish. 
Strata a Kttle older, contain a few fossils of species now ex- 
tinct ; though, usually, species greatly resembling extant ones- 
Of the remains found in strata of still earlier date, the ex- 
tinct species form a larger per centage ; and the differences be- 
tween them and the allied species now living, are more marked. 
That is to say, the gradual change of organic types in Time, 
which we before saw is indicated by the geological record, is 


equally indicated by the relation between existing organic 
types and organic types of the epoch preceding our own. 
The evidence completely accords with the belief in a descent 
of present life from past life. Doubtless such a 

kinship is not incongruous with the doctrine of special crea. 
tions. It may be argued that the introduction, from time to 
time, of new species better fitted to the somewhat changed 
conditions of the Earth's surface, would result in an apparent 
alliance between our living Flora and Fauna, and the Floras 
and Faunas that lately lived. No one can deny it. But on 
passing from the most general aspect of the alliance, to its 
more special aspects, we shall find this interpretation com- 
pletely negatived. 

For besides a close kinship between the aggregate of sur« 
viving forms and the aggregate of forms that have died out 
in recent geologic times ; there is a peculiar connexion of 
like nature between present and past forms in each great 
geographical region. The instructive fact before cited from 
Mr Darwin, is the " wonderful relationship in the same con- 
tinent between the dead and the living." This relationship 
is not explained by the supposition that new species have 
been at intervals supematurally placed in each habitat, as the 
habitat became modified ; since, as we saw, species are by no 
means uniformly found in the habitats to which they are best 
adapted. It cannot be said that the marsupials imbedded in 
recent Australian strata, having become extinct because of 
unfitness to some new external condition, the existing mar- 
supials were then specially created to fit the modified en- 
vironment ; since sundry animals found elsewhere, are 
so much more completely in harmony with these new 
Australian conditions, that, when taken to AustraKa, they 
rapidly extrude the marsupials. While, therefore, the simi- 
larity between the existing Australian Fauna and the Fauna 
which immediately preceded it over the same area, is just 
that which the belief in evolution leads us to expect ; it 
is a similarity which cannot be otherwise accoimted for. 


And so IS it with parallel relations in New Zealand, in South 
America, and in Europe. 

§ 142. Given, then, that pressure which species exercise 
on one another, in consequence of the universal overfilling of 
their respective habitats — ^given the resulting tendency to 
thrust themselves into one another's areas, and media, and 
modes of life, along such lines of least resistance as from 
time to time are foimd — given besides the changes in modes 
of life, hence arising, those other changes which physical 
alterations of habitats necessitate — given the structural 
modifications directly or indirectly produced in organisms 
by modified conditions ; and the facts of distribution in 
Space and Time are accounted for. That divergence and re- 
divergence of organic forms, which we saw to be shadowed . 
forth by the truths of classification and the truths of embry- 
ology, we see to be also shadowed forth by the truths of 
distribution. If that aptitude to multiply, to spread, to 
separate, and to difierentiate, which the human races have in 
aU times shown, be a tendency common to races in general, 
as we have ample reason to assume ; then there will result 
that kind of relation among the species, and genera, and 
orders, peopUng the Earth's surface, which we find exists. 
Those remarkable identities of type discovered between or- 
ganisms inhabiting one medium, and strangely-modified or- 
ganisms inhabiting another medium, are at the same time 
rendered comprehensible. And the appearances and disap- 
pearances of species which the geological record shows us, as 
well as the connexions between successive groups of species 
from early eras down to our own, cease to be inexplicable. 




§ 143. Already it has been necessary to speak of the 
causes of organic evolution in general terms ; and now we 
are prepared for considering them specifically. The task 
before us is to deduce the leading facts of organic evolution, 
from those same first principles which evolution at large 
conforms to. 

Before attempting this, however, it will be instructive to 
glance at the causes of organic evolution that have been 
from time to time alleged. 

§ 144. The theory that plants and animals of all kinds 
were gradually evolved, seems to have been at first accom- 
panied only by the vaguest conception of cause— or rather, 
by no conception of cause properly so called, but only by the 
blank form of a conception. One of the earliest who in 
modem times (1735) contended that organisms are indefi- 
nitely modifiable, and that through their modifications they 
have become adapted to various modes of existence, was 
De Maillet. But though De Maillet supposed all Kving j 

beings to have arisen by a natural, continuous process, he 
does not ayipeax to have had any definite idea of that which 
determines this process. In 1794, in his Zoonomia, 

Dr Darwin gave reasons (sundry of them valid ones) for 
believing that organized beings of every kind, have do- 


Bcended from one, or a few, primordial germs ; and along 
with some observable causes of modification, wliich be points 
out as aiding the developmental process, he apparently 
ascribes it, in part, to a tendency given to such germ or 
germs when created. He suggests the possibility " that all 
warm-blooded a-nimals have arisen from one living filament, 
which The Great First Cause endued with animality, with 
the power of acquiring new parts, attended with new pro- 
pensities, directed by irritations, sensations, volitions, and 
associations ; and thus possessing the faculty of continuing 
to improve by its own inherent activity." In this passage 
we see the idea to be, that evolution is pre-determined 
by some intrinsic proclivity. " It is curious," says 

Mr Charles Darwin, "how largely my grandfather, Dr 
Erasmus Darwin, anticipated the erroneous grounds of 
opinion, and the views of Lamarck." One of the anticipa- 
tions was this ascription of development to some inherent 
tendency. To the " plan g^n^ral de la nature, et sa marche 
uniforme dans ses operations," Lamarck attributes "la 
progression ^vidente qui existe dans la composition de 
rorganisation des animaux ; " and " la gradation r^guliere 
qu'ils devroient offirir dans la composition de leur organ- 
isation," he thinks is rendered irregular by secondary 
causes. Essentially the same in kind, though some- 

what different in form, was the conception put forth in the 
Vestiges of Creation; the author of which • contends "that 
the several series of animated beings, from the simplest and 
oldest up to the highest and most recent, are, under the pro- 
vidence of God, the results, first, of an impulse which has 
been imparted to the forms of life, advancing them, in defi- 
nite times, by generation, through grades of organization 
terminating in the highest dicotyledons and vertebrata ; '' 
and that the progression resulting from these impulses, is 
modified by certain other causes. The broad general con- 
trasts between lower and higher forms of life, are regarded 
by him as due to an innate aptitude to give birth to forms 

26 • 


of more perfect structures. The last to re-enun- 

ciate this doctrine has been Prof. Owen ; who asserts " the 
axiom of the continuous operation of creative power, or of 
the ordained becoming of Kving things." Though these 
highly-general expressions do not suggest any very definite 
idea, yet they imply the belief that organic progress is a 
result of some in-dwelling tendency to develop, supematur- 
ally impressed on living matter at the outset — some ever- 
acting constructive force, which, independently of other 
forces, moulds organisms into higher and higher forms. 

In whatever way it is formulated, or by whatever language 
it is obscured, this ascription of organic evolution to some 
aptitude naturally possessed by organisms, or miraculously 
imposed on them, is unphilosophical. It is one of those ex- 
planations which explains nothing — a shaping of ignorance 
into the semblance of knowledge. The cause assigned is not 
a true cause — not a cause assimilable to known causes — ^not 
a oause that can be anywhere shown to produce analogous 
effects. It is a cause unrepresentable in thought: one of 
those illegitimate symbolic conceptions which cannot by any 
mental process be elaborated into a real conception. In 
brief, this assumption of a persistent formative power, in- 
herent in organisms, and making them unfold into higher 
forms, is an assumption no more tenable than the assump- 
tion of special creations : of which, indeed, it is but a modi- 
fication ; differing only by the fusion of separate unknown 
processes into a continuous unknown process. 

§ 145. Along with this intrinsic tendency to progress, 
supposed to be primordially impressed on them, Dr Darwin 
held that animals have a capacity for being modified by pro- 
cesses which their own desires initiate. He speaks of 
powers as "** excited into action by the necessities of the 
creatures which possess them, and on which their existence 
depends ; " and more specifically he says that " firom their 
first rudiment or primordium, to the termination of their 


lives, all animals undergo perpetual transformations ; wliich. 
are in part produced by their own exertions, in consequence 
of their desires and aversions, of their pleasures and their 
pains, or of irritations, or of associations ; and many of these 
acquired forms or properties are transmitted to their pos* 
terity." While it embodies a belief for which a great deal 
is to be said, this passage involves the assumption that 
desires and aversions, existing before experiences of the ac- 
tions to which they are related, were the originators of the 
actions, and therefore of the structural modifications caused 
by them. In his Philosophie Zoologique^ Lamarck 

much more specifically asserts ''le sentiment inteneur,^' 
to be in all creatures that have developed nervous sys- 
tems, an independent cause of those changes of form which 
are due to the exercise of organs: distinguishing it from 
that simple irritability possessed by inferior animals, which 
cannot produce what we call a desire or emotion ; and 
holding that these last, along with all "qui manquent 
de systeme nerveux, ne vivent qu'A Taide des excitations 
qu'ils refoivent de Texterieur." Afterwards he says — "je 
reconnus que la nature, obligee d'abord d'emprunter des 
milieux environnans la puissance excitatrice des mouvemens 
vitaux et des actions des animaux imparfaits, sut, en com- 
posant de plus en plus Torganisation animale, transporter cette 
puissance dans Tint^rieur m^me de ces fetres, et qu'A la fin, 
elle parvint d mettre cette meme puissance & la disposition 
de rindividu." And still more definitely he contends that 
if one considers " la progression qui se montre dans la com- 
position de Torganisation," ♦ ♦ ♦ " alors on eAt pu aperce- 
voir comment les hesoins, d'abord reduits d nullity, et dont 
le nombre ensuite s'est accru graduellement, ont amen^ le 
penchant aux actions propres d y satisfaire; comment les 
actions devenues habituelles et ^nergiques, ont occasionn^ le 
d^veloppement des organes qui les ex^cutent." 

Now though this conception of Lamarck is more precisely 
stated, and worked out with much greater ela,boration and 


wider knowledge of the facts, it is essentially the same as 
that of Dr Darwin ; and along with the truth it contains, 
contains also the same error more distinctly pronounced. 
Merely noting that desires or wants, acting directly only 
on the nervo-muscular system, can have no immediate in- 
fluence on very many organs, as the viscera, or such external 
appendages as hair and feathers; and observing, further, 
that even some parts which belong to the apparatus of 
external action, such as the bones of the skull, cannot be 
made to grow by increase of ftmction called forth by desire ; it 
will suffice to point out that the difficulty is not solved, but 
simply slurred-over, when needs or wants are introduced as 
independent causes of evolution. True though it is, as Dr 
Darwin and Lamarck contend, that desires, by leading to 
increased actions of motor organs, may induce fiirther de- 
velopments of Qi^h organs ; and true as it probably is, that 
the modifications hence arising, are transmissible to offiipring ; 
yet there remains the unanswered question — ^Whence do these 
desires originate ? The transferrence of the exciting power 
from the exterior to the interior, as described by Lamarck, 
begs the question. -How comes there a wish to perform an 
action not before performed ? Until some beneficial result has 
been felt from going through certain movements, what can 
suggest the execution of such movements? Every desire 
consists primarily of a mental representation of that which 
is desired, and secondarily excites a mental representation of 
the actions by which it is attained ; and any such mental 
representations of the end and the means, imply antecedent 
experience of the end and antecedent use of the means. To 
assume that in the course of evolution there from time to 
time arose new kinds of actions dictated by new desires, is 
simply to remove the difficulty a step back. 

§ 146. Changes of external conditions are named by Dr 
Darwin, as causes of modifications in organisms. Assigning, 
as evidence of original kinship, that marked similarity of 


t jpe which exists among animals^ he regards their devia- 
tions from one another, as caused by differences in their 
modes of life: such deviations being directly adaptive. 
Enumerating various appliances for procuring food, he says 
they all " seem to have been gradually produced during many 
generations by the perpetual endeavour of the creatures to 
supply the want of food, and to have been delivered to their 
posterity with constant improvement of them for the pur- 
poses required." And the creatures possessing these va- 
rious appliances, are considered as having been rendered 
unlike, by seeking for food in unlike ways. As illustrating 
the alterations wrought by changed circumstances, he names 
the acquired characters of domestic animals. La- 

marck has elaborated the same view in detail : using for the 
purpose, with great ingenuity, his extensive knowledge of 
the animal kingdom. From a passage in the Avertissement, 
it would at first sight seem, that he looks aipon direct adapt- 
ation to new conditions, as the chief cause of evolution. He 
says — "Je regardai comme certain que le mouvement des 
fluides dans Tint^rieur des animaux, mouvement qui c'est 
progressivement acc^l^r^ avec la composition plus grande de 
Torganisation ; et que Vinfluence des eirconstances nouvelles, 
& mesure que les animaux s'y expos^rent en se r^pandant 
dans touB les lieux habitables, furent les deux causes g^n^- 
rales qui ont amen^ les diff^rens animaiix d T^tat oii nous les 
voyons actuellement." But elsewhere, the view he expresses 
appears decidedly different from this. He asserts that "dans 
sa marche, la nature a commence, et recommence encore tous 
les jours, par former les corps organises les plus simples ; " 
and that "les premieres ^bauches de Tanimal et du v^g^tal 
£tant form^es dans les lieux et les eirconstances convenables, 
les facult^s d'une vie commen9ante et d'un mouvement or- 
ganique ^tabli, ont n^cessairement d^velopp^ peu d peu les 
organes, et qu'avec le temps elles les ont diversifies ainsi que 
les parties." And then, further on, he puts in italics this 
"proposition:^'' La progression dans la composiUon de Vor^ 


gcmisation sulit, ga et la, dans la aerie gSnirale des cmima/ux, 
des anomalies operees pa/r Vinfluence des circonsta/nces d^hubi- 
tatum, et pa/r celle des habitudes contractees" These, and 
sundry other passages, joined with his general scheme of 
classification, make it clear that Lamarck conceived adaptive 
modification to be, not the cause of progression, but the 
cause of irregularities in progression. The inherent tend- 
ency which organisms have, to develop into more perfect 
forms, would, according to him, result in a uniform series of 
forms ; but varieties in their conditions work divergences of 
structure, which break up the series into groups: groups 
which he nevertheless places in uni-serial order, and regards 
as still substantially composing an ascending succession. 

§ 147. These specidations, crude as they may be considered, 
show much sagacity in their respective authors, and have 
done good service. Without embodying the truth in a de- 
finite shape, they contain adumbrations of it. Not directly, 
but by successive approximations, do mankind reach correct 
conclusions ; and those who first think in the right direction, 
loose as may be their reasonings, and wide of the mark as 
their inferences may be, yield indispensable aid by framing 
provisional conceptions, and giving a bent to inquiry. 

Contrasted with the dogmas of his age, the idea of De 
Maillet was a great advance. Before it can be ascertained 
how organized beings have been gradually evolved, there 
must be reached the conviction that they have been gradu- 
ally evolved; and this conviction he reached. His wild 
notions as to the way in which natural agencies acted in the 
production of plants and animals, must not make us forget 
the merit of his intuition that animals and plants were pro- 
duced by natural causes. In Dr Darwin's brief ex- 
position, the belief in a progressive genesis of organisms, is 
joined with an interpretation having considerable definite- 
ness and coherence. In the space of ten pages he not only 
indicates several of the leading classes of facts which support 


the hypothesis of evolution,. but he does something towards 
elucidating the process of evolution. His reasonings show 
us an unconscious mingling of the belief in a supematurally- 
impressed tendency to develop, with the belief in a develop- 
ment arising from the changing incidence of conditions. 
Probably had he pursued the inquiry fiirther, this last belief 
would have grown at the expense of the first. La- 

marck, in elaborating this general conception, has given 
greater precision to both its truth and its error. Asserting 
the same imaginary factors and the same real factors, he has 
traced out their supposed actions in detail ; and has, in con- 
sequence, committed himself to a greater number of un- 
tenable positions. But while, in trying to reconcile the 
facts with a theory which is only an adumbration of the 
truth, he laid himself open to the criticisms of his con- 
temporaries ; he proved himself profounder than his con- 
temporaries, by seeing that evolution, however caused, has 
been going on. If they were wise in not indorsing a theory 
which fails to account for a great part of the facts ; they 
were unwise in ignoring that degree of congruity with the 
facts, which shows the theory to contain some fimdamental 

Leaving out, however, the imaginary factors of evolution 
which these speculations allege, and looking only at the one 
actual factor which Dr Darwin and Lamarck assign as 
accounting for some of the phenomena ; it is manifest from 
our present stand-point, that this, so far as it is a cause of 
evolution, is a proximate cause and not an ultimate cause. 
To say that functional adaptation to conditions, produces 
either evolution in general, or the irregidarities of evolution, 
is to raise the further question — ^why is there a fimctional 
adaptation to conditions P — ^why do use and disuse generate 
appropriate changes of structure ? Neither this nor any other 
interpretation of biologic evolution which rests simply on the 
basis of biologic induction, is an ultimate .interpretation. The 
biologic induction must itself be interpreted. Only when 


the process of evolution of organisms, is affiliated on tlie 
process of evolution in general, can it be truly said to be 
explained. The thing required is to show that its various 
results are corollaries from first principles. We have to 
reconcile the facts with the universal laws of the re-distribu- 
tion of matter and motion. 



§ 148. When illustrating the rhytliin of motion (First 
Principles, § 94) it was pointed out that besides the daily 
and annual alternations in the quantities of light and heat 
which any portion of the Earth's surface receives from the 
Sun, there are alternations which require immensely-greater 
periods to complete. Reference was made to the fact, that 
" every planet, during a certain long period, presents more of 
its northern than of its southern hemisphere to the Sun at the 
time of its nearest approach to him ; and then again, during 
a like period, presents more of its southern hemisphere than 
of its northern — ^a recurring co-incidence which, though 
causing in some planets no sensible alterations of climate, in- 
volves in the case of the Earth an epoch of 21,000 years, 
during which each hemisphere goes through a cycle of tem- 
perate seasons, and seasons that are extreme in their heat 
and cold." Further, it was pointed out that there is a varia- 
tion of this variation. The slow rhythm of temperate and in- 
temperate climates, which takes 21,000 years to complete, 
itself undergoes exaggeration and mitigation, during epochs 
that are far longer. The Earth's orbit slowly alters in 
form: now approximating to a circle; and now becoming 
more eccentric. During the period at which the Earth's 
orbit has least eccentricity, the temperate and intemperate 
climates which repeat their cycle in 21,000 years, are 


Beyerally less temperate and less intemperate, than wlien^ 
some one or two millions of years later, the Earth's orbit has 
reached its extreme of eccentricity. 

Thus, besides those daily variations in the quantities of light 
and heat received by organisms, and responded to by- varia- 
tions in their functions ; and besides the annual variations in 
the quantities of light and heat which organisms receive, 
and similarly respond to by variations in their fimctions ; 
there are variations that severally complete themselves in 
21,000 years and in some millions of years — variations to 
which there must also be a response in the changed functions 
of organisms. The whole vegetal and animal kingdoms, 
are subject to a quadruply-compoimded rhythm in the in- 
cidence of the forces on whic^ life primarily depends — ^a 
rhythm so involved in its slow working round, that at 
no time during one of these vast epochs, can the in- 
cidence of these forces be exactly the same as at any other 
time. To the direct effects so produced on organ- 

isms, have to be added much more important indirect effects. 
Changes of distribution must result. Certain redistributions 
are occasioned even by the annual variations in the quantities 
of the solar rays received by each part of the Earth's sur&ce. 
The migrations of birds thus caused, are . familiar. So too 
are the migrations of certain fishes : in some cases firom one 
part of the sea to another ; and in some cases from salt water 
to fresh water. Now just as the yearly changes in the amoimts 
of light and heat falling on each locality, yearly extend 
and restrict the habitats of many organisms that are able to 
move about with some rapidity ; so must these alternations 
of temperate and intemperate climates produce extensions 
and restrictions of habitats. These extensions and restric- 
tions, though slow, will be universal — will affect the habitats 
of stationary organisms as well as those of locomotive ones. 
For if during an astronomic era, there is going on at any 
limit to a plant's habitat, a diminution of the winter's cold 
or summer's heat, which had before stopped its spread at 


that limit; then, though the individual plants are fixed^ 
yet the species will move : the seeds of plants living at the 
limit, will produce individuals that survive beyond the limit. 
The gradual spread so effected, having gone on for some ten 
thousand years, the opposite change of climate will begin to 
cause retreat : the tide of each species will during the one 
half of a long epoch, slowly flow into new regions, and 
then wiU slowly ebb away from them. Further, this rise 
and fall in the tide of each species, will, during far longer 
iutervals, undergo increasing rises and falls and then de- 
creasing rises and falls. There will be an alternation of 
spring tides and neap tides, answering in its period to the 
changing eccentricity of the Earth's orbit. 

These astronomical rhythii^s, therefore, entail on organisms 
unceasing changes in the .incidence of forces in two ways. 
They directly subject them to variations of solar influences, 
in such a maimer that each generation is somewhat differently 
affected. in its functions; and they indirectly bring about 
complicated alterations in the enviromng agencies, by carry- 
ing each species into the presence of new physical conditions. 

§149. The power of geological actions to modify every- 
where the circumstances in which plants and animals are 
placed, is conspicuous. In each locality, denudation slowly 
uncovers different deposits ; and slowly changes the exposed 
areas of deposits already uncovered. Simultaneously, the 
alluvial beds that are being formed, are qualitatively affected 
by these progressive changes in the natures and proportions of 
the strata denuded. The inclinations of surfaces and their 
directions with respect to the Sun, are at the same time 
altered ; and the organisms existing on them are thus having 
their thermal conditions continually altered, as well as their 
drainage. Igneous action, too, complicates these gradual 
modifications. A flat region cannot be step by step thrust 
up into a protuberance, without unlike climatic changes 
being produced in its several parts, by their exposures to dif- 


fere&t aspects. Extrusions of trap, wherever they take 
place, reyolutioni^e the localities ; both over the areas covered, 
and over the areas on which their detritus is left. And 
where volcanoes are formed, the ashes they occasionally send 
out, modify the character of the soil throughout large sur- 
rounding tracts. 

In like manner alterations in the Earth's crust, cause the 
ocean to be ever subjecting the organisms it contains to new 
combinations of conditions. Here the water is being deep- 
ened by subsidence, and there shallowed by upheaval. While 
the faUing upon it of sediment brought down by neighbour- 
ing large rivers, is raising the sea-bottom in one place ; in 
another, the habitual rush of the tide is carrying away the 
sediment previously deposited. - The mineral character of 
the submerged surface on which sea- weeds grow and molluscs 
crawl, is everywhere occasionally changed: now by the 
bringing away from an adjacent shore some previously un- 
touched strata; and now by the accumulation of organic 
remains, such as the shells of pteropods or of foraminifera. 
A fiirther series of alterations in the circumstances of marine 
organisms. Is entailed by changes in the movements of the 
water. Each modification in the outlines of neighbouring 
shores, makes the tidal streams vary their directions or 
velocities, or both. And the local temperature is from time 
to time raised or lowered, because some far-distant re-ar- 
rangement of the Earth's crust, has wrought a divergence in 
those circulating currents of warm and cold water which 
pervade the ocean. 

These geologically-caused changes in the physical charac- 
ters of each environment, occur in ever-new combinations, and 
with ever-increasing complexity. As already shown {First 
Principles, § 118), it follows from the law of the multiplication 
of effects, that during long periods, each tract of the Earth's 
surface increases in heterogeneity of both form and substance. 
Hence plants and animals of all kinds, are, in the course of 
generations, subject by these alterations in the crust of the 


Earth, to sets of incident forces which diflfer from previous 
sets, both by changes in the proportions of the factors, and, 
occasionally, by the addition of new factors. 

§ 150. Variations in the astronomical conditions joined 
with variations in the geological conditions, bring about 
variations in the meteorological conditions. Those extremely 
slow alternations of elevation and subsidence, which there is 
reason to believe take place over immense areas, here pro- 
ducing a continent where once there was a fathomless ocean, 
and there causing wide seas to spread where in a long past 
epoch there stood snow-capped mountains, gradually work 
great atmospheric changes. While yet the highest parts of 
an emerging surface of the Earth's crust, exist as a cluster of 
islands, the plants and animals which in course of time migrate 
to them, have climates that are peculiar to small tracts of 
land Surrounded by large tracts of water. As, by successive 
upheavals, greater areas are exposed, there begin to arise 
sensible contrasts between the states of their peripheral parts 
and their central parts: the sea and land breezes, which 
daily moderate the extremes of temperature near the shores, 
cease to affect the interiors ; and the interiors, less qualified 
too in their heat and cold by such ocean-currents as bathe 
the shores, acquire more decidedly the characters due to 
their latitudes. Along with the further elevations which 
unite the members of the archipelago into a continent, there 
come new meteorologic changes, as well as exacerbations of 
the old. The winds, which were comparatively uniform in 
their directions and periods when only islands existed, grow 
involved in their distribution, and widely-different in dif- 
ferent parts of the continent. The quantities of rain which 
they discharge and of moisture which they absorb, vary 
everywhere according to the proximity to the sea and to 
surfaces of land having special characters. 

Other complications result from variations of height above 
the sea : elevation producing a decrease of heat and conse- 


quently an increase in the precipitation of water — ^a precipit- 
ation l^at takes the shape of snow where the elevation is 
very great^ and of rain where it is not so great. The gather- 
ing of clouds and descent of showers around mountain tops, 
are familiar to every tourist. Inquiries in the neighbouring 
valleys, prove that within distances of a mile or two the 
recurring storms difiTer in their frequency and violence. 
Nay, even a few yards off, the meteorologic conditions vary in 
such regions : as witness the way in which the condensing 
vapour keeps eddying round on one side of some high crag, 
while the other side is clear ; or the way in which the snow- 
line runs irregularly to many different heights, in all the minor 
valleys and ravines and hollows of each mountain side. 

Climatic variations that are thus geologically produced, 
being compounded with those which result from the slow 
astronomical changes; and no correspondence existing be- 
tween the geologic and the astronomic rhythms ; it results 
that the same plexus of actions never recurs. Hence the 
incident forces to which the organisms of every locality are 
exposed by atmospheric agencies, are ever passing into un- 
paralleled combinations ; and these are on the average ever 
becoming more complex. 

§ 151. Besides changes in the incidence of inorganic 
forces, there are equally continuous, and still more involved, 
changes in the incidence of forces which organisms exercise 
on one another. As before pointed out (§ 105), the plants 
and animals inhabiting each locality, are held together in so 
entangled a web of relations, that any considerable modifica- 
tion which one species undergoes, acts indirectly on many 
other species ; and eventually changes, in some degree, the 
circumstances of nearly all the rest. If an increase of heat, 
or modification of soil, or decrease of humidity, causes a par- 
ticular kind of plant either to thrive or to dwindle ; an 
unfavourable or favourable effect is wrought on all such 
competing kinds of plants, as are not immediately influenced 



in the same way. The animals which eat the seeds or browse 
on the leaves either of the plant primarily aflfected or those of 
its competitors, are severally altered in their states of nutri- 
tion and in their numbers ; and this change presently tells 
on various predatory animals and parasites. And since each 
of these secondary and tertiary changes, becomes itself a 
centre of others; the increase or decrease of each species, 
produces waves of influence which spread and reverberate 
and re-reverberate, throughout the whole Flora and Fauna 
of the locality. 

More marked and multiplied still, are the ultimate effects 
of those causes which make possible the colonization of neigh- 
bouring areas. Each intruding plant or animal, besides the 
new inorganic conditions to which it is subject, is subject to 
organic conditions considerably different from those to which 
it has been habituated. It has to compete with some organ- 
isms unlike those of its preceding habitat. It must preserve 
itself from enemies not before encountered. Or it may meet 
with a species over which it has some advantage greater 
than any that it had over the species it was previously in 
contact with. Even where migration does not bring it face 
to face with new competitors or new enemies or new prey, 
it inevitably experiences new proportions among these. 
Further, an expanding species is almost certain to invade 
more than one adjacent region. Spreading north or south, it 
will come among the plants and animals, here of a* level 
district and there of a hilly one — ^here of an inland tract, 
and there of a tract bordered by the sea. And while differ- 
ent groups of its members will thus expose themselves to 
the actions and re-actions of different Floras and Faunas, 
these different Floras and Faunas will simultaneously have 
their organic conditions changed by the intruders. 

This process becomes gradually more active and more 
complicated. Though in partictdar cases, a plant or animal 
may fall into simpler relations with the living things around, 
than those it was before placed in ; yet it is manifest that, 



on the average, the organic environments of orgaiuBms have 
been increasing in heterogeneity. As the number of species 
with which each species is directly or indirectly implicated^ 
multiplies, each species is ofkener subject to changes in the 
organic actions which influence it. These more frequent 
changes severally grow more involved. And the corre- 
sponding reactions affect larger Floras and Faunas, in ways 
increasingly complex and varied. 

§ 162. When the astronomic, geologic, meteorologic, and 
organic agencies that are at work on each species of organ- 
ism, are contemplated as becoming severally more compli- 
cated in themselves, and at the same time as co-operating in 
ways that are always more or less new ; it will be seen that 
throughout all time, there has been an exposure of organisms 
to endless successions of modifying causes which gradually 
acquire an intricacy that is scarcely conceivable. Every 
kind of plant and animal may be regarded as for ever pass- 
ing into a new environment — as perpetually having its 
relations to external circumstauces altered, either by their 
changes with respect to it when it remains stationary, or by 
its changes with respect to them when it migrates, or by 

Yet a further cause of progressive alteration and compK- 
cation in the incident forces, exists. * All other thiags con- 
tinuing the same, every additional faculty by which an 
organism is brought into relation with external objects, as 
well as every improvement in such faculty, becomes a means 
of subjecting the organism to a greater niunber and variety 
of external stimuli, and to new combinations of external 
stimuli. So that each advance in complexity of organization, 
itself becomes an added source of complexity in the incidence 
of external forces. 

Once more, every increase in the locomotive powers of 
animals, increases both the multiplicity and the multiformity 
of the actions of things upon them, and of their reactions 


upon things. Poubling a creature's activity, quadruples the 
area that comes within the range of its excursions: thus 
augmenting in number and heterogeneity, the external 
agencies which act on it during any given interval. 

By compounding the actions of these several orders of 
factors, there is produced a geometric progression of changes, 
increasing with immense rapidity. And there goes on an 
equally rapid increase in the frequency with which the 
combinations of the actions are altered, and the intricacies 
of their co-operations enhanced. 




§ 153. We saw at the outset (§§ 10—16), that organic 
matter is built up of molecules so extremely unstable, that 
the slightest variation in their conditions destroys their 
equilibrium ; and causes them either to assume altered 
structures or to decompose. But a substance which is beyond 
all others changeable by the actions and reactions of tho 
forces liberated from iostant to instant within its own 
mass, must be a substance that is beyond all others change- 
able by the forces acting on it from without. If their 
composition fits organic aggregates for undergoing with 
special facility and rapidity those re-distributions of matter 
and motion whence result individual organization and life ; 
then their composition must make them similarly apt to 
undergo those permanent re-distributions of matter and mo- 
tion which are expressed by changes of structure, in corre- 
spondence with permanent re-distributions of matter and 
motion in their environments. 

Already in First Principles, when considering the phe- 
nomena of Evolution in general, the leading characters and 
causes of those changes which constitute organic evolution, 
were briefly traced. Under each of the derivative laws of 
force to which the passage from an incoherent, indefinite 
homogeneity to a coherent, definite heterogeneity, conforms, 
were given illustrations drawn from the metamorphoses of 


living bodies. Here it will be needful to contemplate the 
several resulting processes as going on at once, in both 
individuals and species. 

§ 154. Our postulate being that organic evolution in ge- 
neral commenced with homogeneous organic matter, just as 
the evolution of individual organisms commences, we have 
first to remember that the state of homogeneity is an un- 
stable state (First Prmdples, § 109). In any aggregate 
"the relations of outside and inside, and of comparative 
nearness to neighbouring sources of influence, imply the re- 
ception of influences that are unlike in quantity or quality, 
or both ; and it follows that unlike changes will be produced 
in the parts thus dissimilarly acted upon." Further, "if 
any given whole, instead of being absolutely uniform through- 
out, consists of parts distinguishable from each other — ^if 
each of these parts, while somewhat unlike other parts, is 
uniform within itself; then, each of them being in imstable 
equilibrium, it follows that while the changes set up within 
it must render it multiform, they must at the same time 
render the whole more multiform than before ; " and hence, 
" whether that state with which we commence be or be not 
one of perfect homogeneity, the process must equally be 
towards a relative heterogeneity." This loss of 

homogeneity which the special instability of organic aggre- 
gates fits them to display more promptly and variously than 
any other aggregates, must be shown in more nimierous 
ways in proportion as the incident forces are more numerous. 
Every difierentiation of structure being a result of some 
diflerence in the relations of the parts to the agencies acting 
on them, it follows that the more multiplied and more unlike 
the agencies, the more varied must be the differentiations 
wrought. Hence the gravitation from a state of homogeneity 
to a state of heterogeneity, will be conspicuously shown in 
proportion as the enviroimient is complex. This 

transition from a uniform to a multiform state, must con- 


tinue through successive individuals. Given a series of or- 
ganisms, each of which is developed from, a portion of a 
preceding organism, and the question is, whether, after 
exposure of the series for a milUon years to changed incident 
forces, one of its members will be the same as though the 
incident forces had only just changed. To say that it will, 
is implicitly to deny the persistence of force. In relation to 
any cause of divergence, the whole series of such organisms 
may be considered as fosed together into a continuously- 
existing organism; and when so considered, it becomes 
manifest that a continuously-acting cause will go on working 
a continuously-increasing effect, until some countera<;ting 
cause prevents any further effect. 

But now if any primordial organic aggregate, must, in itseK 
and through its descendants, gravitate finom uniformity to 
multiformity, in obedience to the more or less multiform 
forces acting on it ; what must happen if these multiform 
forces are themselves ever undergoing slow variations and 
complications P Clearly the process, ever-advancing towards 
a temporary limit but ever having its limit removed, must 
go on unceasingly. On those structural changes wrought 
in the once homogeneous aggregate by an original set of in- 
cident forces, will be superposed further changes wrought 
by a modified set of incident forces ; and so on throughout 
all time. Omitting for the present those circumstances 
which check and qualify its consequences, the instability of 
the homogeneous must be recognized an ever-acting cause of 
organic evolution, as of all other evolution. 

While it follows that every organism, considered as an in- 
dividual and as one of a series, tends thus to pass into a more 
heterogeneous state ; it also follows that every species, con- 
sidered as an aggregate of individuals, tends to do the like. 
Throughout the area it inhabits, the conditions can never 
be absolutely miiform : its members must, in different parts 
of its area, be exposed to different sets of incident forces. 
Still more decided must this difference of exposure be when 


its members spread into other habitats. Those expansive 
and repressive energies which set to each species a limit that 
perpetually oscillates from side to side of a certain mean, are, 
as ^we lately saw, frequently changed by new combinations 
of the external factors — astronomic, geologic, meteorologic, 
and organic. Hence there ftem time to time arise lines of di- 
minished resistance, along which the species flows into new 
localities. Such portions of the species as thus migrate, are 
subject to circumstances markedly contrasted with its average 
circumstances. And from multiformity of the circumstances, 
mujst come multiformity of the species. 

Thus the law of the instability of the homogeneous, has here 
a three-fold corollary. As interpreted in connexion with the 
ever-progressing, ever-complicating changes in external fac- 
tors, it brings us to the conclusion that there must be a pre- 
vailing tendency towards greater heterogeneity in all kinds 
of organisms, considered both individually and in successive 
generations ; as well as in each assemblage of organisms con- 
stituting a species; and, by consequence, in each genus, 
order, and class. 

§ 155. When considering the causes of evolution in 
general, we further saw {First PHnciples, § 116), that the 
multiplication of effects aid^ continually to increase sthat 
heterogeneity into which homogeneity inevitably lapses.'^It 
was pointed out that since " the several parts of an aggre- 
gate are differently modified by any incident force ; " and 
that since " by the reactions of the differently modified parts 
the incident force itself must be divided into differently 
modified parts ; " it follows that " each differentiated di- 
vision of the aggregate thus becomes a centre fix)m which 
a differentiated division of the original force is again 
diffused. And since unlike forces must produce imlike 
results, each of these differentiated forces must produce, 
throughout the aggregate, a ftirther series of differentia- 
tions.'' And to this it was added, that in proportion as 


the heterogeneity increases, the complications arising from 
this multiplication of effects grow more marked; since 
the more strongly contrasted the parts of an aggregate 
become, the more different must be their reactions upon 
incident forces, and the more unlike must be the secondary 
sets of effects which these modified incident forces initiate ; 
and since every increase in the number of unlike parts 
increases the number of such differentiated incident forces, 
and such secondary sets of effects. 

How this multiplication of effects conspires with the in- 
stability of the homogeneous^ to work an increasing multi- 
formity of structure in an organism, was shown at the time ; 
and the foregoing pages contain further incidental illustra- 
tions. Under the head of Adaptation (§ 69), it was shown 
that a change in one fiinction must act and re-act through 
ever-complicating perturbations on the rest; and that, eventu- . 
ally, all parts of the organism must be modified in their 
states. Suppose that the head of a mammal becomes very 
much more weighty — ^what must be the indirect results? 
The muscles of the neck are put to greater exertions ; and 
its yertebrsB have to bear additional tensions and pressures, 
caused both by the increased weight of the head, and the 
stronger contractions of the muscles that support and move the 
head. These muscles also affect their own attachments: several 
of the dorsal spines have augmented strains put on them ; 
and the vertebrae to w:hich they are fixed, are more severely 
taxed. Further, this heavier head and the more massive 
neck it necessitates, require a stronger fulcrum : the whole 
thoracic arch, and the fore limbs which support it, are sub- 
ject to greater continuous stress and more violent occasional 
shocks. And the required strengthening of the fore-quarters 
cannot take place, without, the centre of gravity being 
changed, and the hind limbs being differently reacted upon 
during locomotion. Any one who compares the outline 
of the bison with that of its congener, the ox, will clearly 
see how profoundly a heavier head affects the entire osseous 


and musculax systems. Besides this multiplica- 

tion of meclianical effects^ there is a multiplication of 
physiological effects. The vascular apparatus is modified 
throughout its whole structure, by each considerable modifi- 
cation in the proportions of- the body. Increase in the size 
of any organ, implies a quantitative, and often a qualitative, 
reaction on the blood ; and so alters the nutrition of all other 
organs. Such physiological correlations are exemplified in the 
many differences that accompany difference of sex. That the 
minor sexual peculiarities are brought about by the physio- 
logical actions and reactions, is shown both by the fact that 
they are commonly but faintly marked until the fundamentally 
distinctive organs are developed; and that when the de- 
velopment of these is prevented, the minor sexual peculiarities 
do not arise. No ftirther proof is, I think, needed, 

that in any individual organism or its descendants, a new 
external action must, besides the primary internal change 
which it works, work simdry secondary changes, as well as 
tertiary changes still more multiplied. That tendency to- 
wards greater heterogeneity which is given to an organ- 
ism by disturbing its environment, is helped by the tendency 
which every modification "has to produce other modifications 
— ^modifications which must become more numerous in pro- 
portion as the organism becomes more complex. And 
then, lastly, among the indirect and involved manifestations 
of this tendency, we must not omit the innimierable small 
irregularities of structure that result from the crossing of 
dissimilarly-modified individuals. It was shown (§§ 89, 90) 
that what are called "spontaneous variations," are inter- 
pretable as results of miscellaneously compounding the 
changes wrought in different lines of ancestors by different 
conditions of Kfe. These still more complex and multi- 
tudinous effects so produced, are thus further illustrations of 
the multiplication of effects. 

Equally in the aggregate of individuals constituting a 
species, does multiplication of effects become the continual 


cause of increasiiig multiformity. . The lapse of a species into 
divergent varieties, initiates fresh combinations of forces 
tending to work further divergences. The new varieties 
compete with the parent species in new ways ; and so add new 
elements to its circumstances. They modify somewhat the 
conditions of other species existing in their habitat, or into 
whose habitat they have spread; and the modifications 
wrought in such other species, become additional sources of 
influence. The Flora and Fauna of every region are united 
by their entangled relations into a whole, of which no part 
can be affected without affecting the rest. Hence, each dif- 
ferentiation in a local assemblage of species, becomes the 
cause of fiirther differentiations in such assemblage. 

§ 156. One of the universal principles to which we saw 
that the re-distribution of matter and motion conforms, is 
that in any aggregate made up of mixed units, incident 
forces produce segregation — separate unlike units and unite 
like units ; and it was shown that the increasing integration 
and definiteness which characterizes each part of an evolving 
organic aggregate, as of every other aggregate, results from 
this {First Principles, § 126). It remains here to be 
pointed out, that while the actions and reactions going on 
between organisms and their ever-changing environments, 
add to the heterogeneity of organic structures, they also 
give to the heterogeneity this growing distinctness. At 
first sight the reverse might be inferred. It might be argued 
that any new set of effects wrought in an organism by some 
new set of external forces, must tend more or less to obliter- 
ate the effects previously wrought — ^must produce confrision 
or indefiniteness. A little consideration, however, will dissi- 
pate this impression. 

Doubtless the condition imder which alone increasing de- 
finiteness of structure can be acquired by any part of an or- 
ganism, either in an individual or in successive generations, is 
that such part shall be exposed to some set of tolerably-con- 


Btant forces; and doubtless, continual change of circumstances 
interferes with this. But the interference can never be con- 
siderable. For the pre-existing structure of an organism pre- 
vents it &om lining under any new conditions except such as 
are congruous with the ftmdamental characters of its organiza- 
tion — ^such as subject its essential organs to actions substan- 
tially the same as before. Great changes must kill it. Hence, 
it can continuously expose itself^ and its descendants, only to 
those moderate changes which do not destroy the general har- 
mony between the aggregate of incident forces and the ag- 
gregate of its fimctions. That is, it must remain under 
influences calculated to make greater the definiteness of 
the chief 'diflferentiations already produced. If, r for ex- 
ample, we set out with an animal in which a rudimentary 
vertebral column with its attached muscidar system has 
been established; it is clear that the mechanical arrange- 
ments have become thereby so far determined, that sub- 
sequent modifications are extremely likely, if not certain, to 
be consistent with the production of movement by the action 
of muscles on a flexible central axis. Hence, there will con- 
tinue a general similarity in the play of forces to which the 
flexible central axis is subject ; and so, notwithstanding the 
metamorphoses which the vertebrate type imdergoes, there 
wiU be a maintenance of conditions favourable to increasing 
definiteness and integration of the vertebral column. More- 
over, this maintenance of such conditions becomes secure in 
proportion as organization advances. Each further ^com- 
plexity of structure, implying some . further complexity in 
the relations between an organism and its environm^it, must 
tend to specialize the actions and reactions between it and its 
environment — ^must tend to increase the stringency with 
which it is restrained within such environments as admit of 
those special actions and reactions for which its structure fits 
it ; that is, must ftirther guarantee the continuance of those 
actions and reactions to which its essential organs respond, 
and therefore the continuance of the segregating process. 


How in each species, considered as an aggregate of indi- 
viduals, there must arise stronger and stronger contrasts 
between those divergent varieties which result from the 
instability of the homogeneous and the multiplication of 
effects, needs only be briefly indicated. It has already 
been shown {First Prmdjples, § 126), that in conformity to 
the universal law that mixed units are segregated by like 
incident forces, there are produced increasingly-definite 
distinctions among varieties, wherever there occur definitely- 
distinguished sets of conditions to which the varieties are re- 
spectively subject. 

§ 157. Probably in the minds of some, the reading of this 
chapter has been accompanied by a running conmientary, to 
the effect that the argument proves too much. The apparent 
implication is, that the passage from an indefinite, incohe- 
rent homogeneity to a definite, coherent heterogeneity in 
organic aggregates, must have been going on imiversally ; 
whereas we find that in many cases there has been persist- 
ence without progression. This apparent implication, how- 
ever, is not a real one. 

For though every environment on the Earth's surface 
undergoes changes ; and though usually the organisms 
which each environment contains, cannot escape certain 
resulting new influences; yet occasionally such new in- 
fluences are escaped, by the survival of species in the un- 
changed parts of their habitats, or by their spread into 
neighbouring habitats which the change has rendered like 
their original habitats, or by both. Any alteration in the 
temperature of a climate or its degree of humidity, is un- 
likely to affect simultaneously the whole area occupied by a 
species ; and further, it can scarcely fail to happen that the 
addition or subtraction of heat or moisture, will give to a 
part of some adjacent area, a climate like to that to which 
the species has been habituated. If, again, the circumstances 
of a species are modified by the intrusion of some foreign 


kind of plant or animal, it follows that since the intruders 
will probably not spread throughout its whole habitat, the 
species will, in one or more localities, remain unaflFected by 
them. Especially among marine creatures, must there fre- 
quently occur cases in which modifying causes are con- 
tinually eluded. Much more imiform as are the physical 
conditions to which the sea exposes its inhabitants, it becomes 
possible for such of them as live on widely-diffused food, to 
be widely distributed ; and wide distribution generally pre- 
vents the members of a species from being all subject to the 
same cause. Our commonest cirrhiped, for instance, subsisting 
on minute creatures that are everywhere dispersed through 
the sea ; needing only to have some firm surface on which 
to build up its shell ; and in scarcely any danger from sur- 
rounding animals; is able to exist on shores so widely remote 
from one another, that nearly every change in the actions of 
incident forces, must fall within narrower areas than that 
which the species occupies. In nearly every case, therefore, 
a portion of the species will survive unmodified. Its easily- 
transported germs will take possession of such new habitats 
as have been rendered fitter by the change that has unfitted 
some parts of its original habitat. Hence, on successive 
occasions, while some parts of the species are slightly trans- 
formed, another part may continually escape transformation 
by migrating hither and thither, where the simple condi- 
tions needed for its existence recur in nearly the same com- 
binations as before. And it wiU so become possible for it 
to survive, with comparatively trifling structural changes, 
throughout long geologic periods. 

§ 158. The results to which we find ourselves led, are 

In subordination to the different amounts and v kinds of 
forces to which its different parts are exposed, every in- 
dividual organic aggregate, like all other, aggregates, tends 
to pass from its original indistinct simplicity towards a more 


distinct complexity. Unless we deny the persistence of 
force, we must admit tliat the gravitation of an organism's 
structure from an indefinitely homogeneous to a definitely 
heterogeneous state, must he cumulative in successive genera- 
tions, if the forces causing it continue to act. And for the 
like reasons, the increasing assemblage of individuals arising 
from a common stock, is also liable to lose its orig^inal 
tmiformity; and, in successive generations, to grow more 
pronounced in its multiformity. 

These changes, which. would go on to but a comparatively 
small extent were organisms exposed to constant external 
conditions, are kept up by the continual changes in external 
conditions, produced by astronomic, geologic, meteorologic, 
and organic agencies: the average result being, that on 
previous complications of structure wrought by previous 
incident forces, new complications are continually superposed 
by new incident forces. And hence simultaneously arises 
increasing heterogeneity in the structures of individuals, in 
the structures of species, and in the structures of the Earth's 
Flora and Fauna. 

But while, in very many or in most cases, the ever- 
changing incidence of forces is ever adding to the complexity 
of organisms, and to the complexity of the organic world as a 
whole ; it does this only where its action cannot be eluded. 
And since, by migration, it is possible for species to keep 
themselves under conditions that are tolerably constant; 
there must be a proportion of cases in which greater hetero- 
geneity of structure is not produced. 

Uniting these three propositions, we are brought to a con- 
clusion which, so far as it goes, appears to be in harmony 
with the facts. We find progression to result, not from a 
special, inherent tendency of living bodies, but from a general 
average eflFeotrof their relations to surrounding agencies. 
While we are not called on to suppose that there exists in 
organisms any primordial impulse which makes them con- 
tinually imfold into more heterogeneous forms; we see 


that a liability to be unfolded arises from tbe actions and 
reactions between organisms and their fluctuating environ- 
ments. And we see that the existence of such a cause of 
development, presupposes the non-occurrence of development 
where this fluctuation of actions and reactions does not 
come into play. 

To show, however, that there must arise a certain general 
tendency to the production of more heterogeneous aggregates, 
is not sufficient. It is quite conceivable that aggregates 
shoidd be rendered more heterogeneous by changing incident 
forces, without having given to them that peculiar form of 
heterogeneity required for carrying on the functions of life. 
Hence it remains now to inquire, how the production and 
maintenance of this peculiar form of heterogeneity is insured. 



§ 159. Every cliange is of necessity towards a balance of 
forces ; and of necessity can never cease until a balance offerees 
is reached. When treating of equilibration under its general 
aspects (First Principles, Part II., Chap, xvi.), we saw that 
in every aggregate having compound movements, there 
tends continually to be established a moving equilibrium ; 
since any unequilibrated force to which such an aggregate 
is subject, if not of a kind to overthrow the aggregate al- 
together, must continue modifying its state until an equi- 
librium is brought about. And we saw that the structure 
simultaneously reached must be " one presenting an arrange- 
ment of forces that counterbalance all the forces to which the 
aggregate is subject ; " since, " so long as there remains a 
residual force in any direction — be it excess of a force 
exercised by the aggregate on its environment, or of a force 
exercised by its environment on the aggregate, equilibrium 
does not exist ; and therefore the re-distribution of matter 
must continue." 

It is essential that this truth should here be fully under- 
stood ; and to the end of insuring a clear comprehension of 
it, some re-illustration is desirable. The case of the Solar 
System will best serve our purpose. An assemblage of bodies, 
each of which has its simple and compound motions, that 
severally alternate between two extremes, and the whole of 


which has its involved perturbations, that now increase and 
now decrease, is here presented to ns. Suppose a new 
force were brought to bear on this moving equiKbrium — ^say- 
by the arrival of some wandering mass, or by an additional 
momentum given to one of the existing masses — ^what would 
be the result P If the strange body or the extra force were 
very large, it might so derange the entire system as to cause 
its collapse : by overthrow of its rhythmical movements, the 
moving equilibrium might rapidly be changed into a com- 
plete equilibrium. But what if the incident force, falling on 
the system from without, proved insufficient to overthrow itP 
There would then arise a set of perturbations which would, 
in the course of an enormous period, slowly work round into 
a modified moving equilibrium. The effects primarily im- 
pressed on the adjacent masses, and in a smaller degree on 
the remoter masses, would soon become complicated with the 
secondary effects impressed by the disturbed masses on one 
another ; and these again with tertiary effects. Waves of 
perturbation would continue to be propagated throughout 
the entire system ; imtil, around a new centre of gravity, 
there had been established a set of planetary motions more 
or less different from the preceding ones. All this would 
necessarily follow from the truth, that any new force brought 
to bear on a moving equilibrium, must gradually be used up 
in overcoming the forces that resist the divergence it gener- 
ates : which antagonizing forces, being then no longer op- 
posed, set up a counter-action, ending in a compensating 
divergence in the opposite direction, that is followed by a 
re-compensating divergence ; and so on, imtil there is either 
established some additional rhythmical movement, or some 
equivalent modification of the pre-existing rhythmical move- 
ments. Now though instead of being, like the Solar 
System, in a state of independent moving equilibrium, an 
organism is in a state of dependent moving equilibrium 
(First Principles, § 130) ; yet this does not prevent the 
manifestation of the same law. Every animal daily obtains 



from without, a supply of force to replace the force 
which it expends; but this continual giving to its parts a 
new momentum, to make up for the momentum continually 
lost, does not interfere with the carrying on of actions and 
reactions like those just described. Here, as before, we have 
a definitely-arranged aggregate of parts, which we call 
organs, having their definitely-established actions and. re- 
actions, which we call functions. These rhythmical actions 
or functions, and the various compound rhythms resulting 
from their combinations, are in such adjustment as to balance 
the actions to which the organism is subject : there is a con- 
stant or periodic genesis of forces, which, in their kinds, 
amounts, and directions, suffice to antagonize the forces 
which the organism has constantly or periodically to bear. 
If then there exists this state of moving equilibrium among 
a definite set of internal actions, exposed to a definite set of ex- 
ternal actions ; what must result if any of the external actions 
are changed P Of course there is no longer an equilibrium. 
Some force which the organism habitually generates, is too 
great or too small to balance some incident force ; and there 
arises a residuary force exerted by the environment on the 
organism, or by the organism on the environment. This 
residuary force— this unbalanced force, of necessity expends 
itself in producing some change of state in the organism. 
Acting directly on some organ and modifying its function, 
it indirectly modifies dependent functions, and remotely 
influences all the functions. As we have already seen 
(§§ 68, 69), if this new force is permanent, its effects must 
be gradually diffused throughout the entire system ; until it 
has come to be equilibrated in working those structural re- 
arrangements which produce an exactly counterbalancing 

The bearing of this general truth on the question we are 
now dealing with, is obvious. Those modifications upon 
modifications, which the unceasing mutations of their en- 
vironments have been all along generating in organisms, 


have been in each case modifications involved by the 
estabUshment of a new balance with the hew combination of 
conditions. In every species throughout all geologic time, 
there has been perpetually going on a rectification of the 
equilibrium, that has been perpetually disturbed by the 
alteration of surrounding circumstances ; and every further 
heterogeneity has been the addition of a structural change 
entailed by a new equilibration, to the structural changes 
entailed by previous equilibrations. There can be no other 
ultimate interpretation of the matter, since change can have 
no other goal. Any fresh force brought to bear oA an 
aggregate in a state of moving equilibrium, must do one of 
two things: it must either overthrow the moving equi- 
librium altogether, or it must alter without overthrowing it ; 
and the alteration must end in the establishment of a new 
moving equilibrium. Hence in organisms, death or restora- 
tion of the physiological balance, are the only alternatives. 

This equilibration between the functions of an organism 
and the actions in its environment, may be either direct or 
indirect. The new incident force may either immediately 
call forth some counteracting force, and its concomitant 
structural change ; or it may be eventually balanced by some 
otherwise-produced change of fimction and structure. 
These two processes of equilibration are quite distinct, and 
must be separately dealt with. We will devote this chapter 
to the first of them. 

§ 160. Direct equilibration is that process currently 
known as adaptation. We have already seen (Part II., 
Chap, v.), that individual organisms become modified when 
placed in new conditions of life — so modified as to re-adjust 
the powers to the requirements ; and though there is great 
difficulty in disentangling the evidence, we found reason for 
thinking (§ 82) that structural changes thus caused by 
functional changes are inherited. In the last chapter, it 
was argued that if, instead of the succession of individuals 

28 • 


constituting a species, there were a continuously-existing 
individual, any such functional and structural divergence as 
we see produced by a new incident force, would necessarily 
go on increasing until the new incident force was counter- 
poised; and that the replacing of a continuously-existing 
individual by a succession of individuals, each formed out of 
the modified substance of its predecessor, will not prevent the 
like effect from being produced — ^the persistence of force 
negativing any other inference. Here we further find, that 
this limit towards which any such organic change advances, 
in the species as in the individual, is a new moving equi- 
librium adjusted to the new arrangement of external forces. 

But now, what are the conditions under which alone, direct 
equilibration can occur P Are all the modifications that serve 
to re-fit organisms to their environments, directly adaptive 
modifications? And if otherwise, which are the directly 
adaptive and which are not? How are we to distinguish 
between them P 

Manifestly, for any moving equilibrium to be gradually 
altered, it is needful, first, that some force shall operate upon 
it ; and, second, that the force shall not be such as to over- 
throw it. If in the environment there exists some agency 
that would act advantageously on an organism were the or- 
ganism a little modified, but which does not act on it in the 
absence of the required modification; it is clear that this 
agency cannot itself tend to produce the modification. On 
the other hand, if the external agency be of such kind, that 
individuals of the species whenever affected by it, are either 
killed or so injured that the production of vigorous o£&pring 
is much interfered with, there cannot be directly wrought in 
the species, any such alteration as will fit it to cope with 
this external agency. The only new incident forces which 
can work the changes of function and structure required to 
bring any animal or plant into equilibriimi with them, are 
such incident forces as operate on this animal or plant, 
either continuously or frequently. They must be capable 


of appreciably changing that set of complex rhythmical 
actions and reactions constituting the life, of the organism ; 
and yet must not usually produce perturbations that are 
fatal. Let us see what are the limits to direct equilibra- 
tion hence arising. 

§ 161. In plants, organs engaged in nutrition, and exposed 
to variations in the amounts and proportions of matters and 
forces utilized in nutrition, may be expected to undergo cor- 
responding variations. We find evidence that they do this. 
The " changes of habit " which are common in plants, when 
taken to places unlike in climate or soil to those before in- 
habited by them, are changes of parts in which the modified 
external actions directly produce modified internal actions. 
The characters of the stem and shoots as woody or succulent, 
erect or procumbent ; of the leaves in respect of their sizes, 
thicknesses, and textures ; of the roots in their degrees of 
development and modes of growth ; are obviously in imme- 
diate relation to the characters of the environment. A per- 
manent difiference in the quantity of light or heat, affects, day 
after day, the processes going on in the leaves. Habitual 
rain or drought, alters all the assimilative actions, and 
appreciably influences the organs that carry them on. Some 
particular substance, by its presence in the soil, gives new 
qualities to some of the tissues ; causing greater rigidity or 
flexibility, and so affecting the general aspect. Here, then, 
we have, in plants, changes tending to bring about in them, 
modified arrangements of functions and structures, in equi- 
librium with modified sets of external forces. 

But now let us turn to other classes of organs possessed by 
plants — organs which are not at once affected in their actions 
by the variations of incident forces. Take first the organs 
of defence. Many plants are shielded against animals that 
would else devour them, by formidable thorns ; and others, 
like the nettle, by stinging hairs. These must be counted 
among the appliances by which equilibrium is maintained 


between the actions in the orgamsm and the actions in its 
environment; seeing that all other things remaining the 
same, if these defences were absent, the destruction by herb- 
ivorous animals would be so increased, that the number of 
young plants annually produced would not suffice, as it now 
does, to balance the mortality, and the species would there- 
fore disappear. But these defensive appliances, though they 
aid in maintaining the balance between inner and outer 
actions, cannot have been directly called forth by the outer 
actions which they serve to neutralize; for these outer 
actions do not continuously affect the fimctions of the plant 
even in a general way, still less in the special way required. 
Suppose a species of nettle bare of poison-hairs, to be habit- 
ually eaten by some mammal intruding on its habitat ; the 
agency of this mammal would have no direct tendency to 
develop poison-hairs in the plant; since the individuals 
devoured could not bequeath changes of structure, even were 
the actions of a kind to produce them ; and since the in- 
dividuals that perpetuated themselves, would be those on 
which the new incident force had not fallen. An- 

other class of organs similarly circumstanced, are those of 
reproduction. Like the organs of defence, these are not, 
during the life of the individual plant, variably exercised by 
variable external actions; and therefore do not fulfil those 
conditions under which structural changes may be directly 
caused by changes in the environment. The generative 
apparatus contained in every flower, acts only once during 
its existence ; and even then, the parts subserve their ends 
in a passive rather than an active way. Functionally-pro- 
duced modifications are therefore out of the question. If a 
plant's anthers are so placed, that the insect which most 
commonly frequents its flowers, is sure to come in contact 
with the pollen, and to fertilize with it other flowers of the 
same species; and if this insect, dwindling away or dis- 
appearing from the locality, leaves behind no insects that 
have such shapes a id habits as cause them to do the same 


thing efficiently, but only some which do it inefficiently ; it 
is clear that the change of its conditions, has no immediate 
tendency to work in the plant any such structural change 
as shall bring about a new balance with its conditions. For 
the anthers, which, even when they discharge their ftinctions, 
do it simply by standing in the way of the insect, are, under 
the supposed circumstances, left untouched by the insect ; 
and this remaining untouched, cannot have the eflfect of so 
modifying the stamens as to bring the anthers into a position 
to be touched by some other insect. Only those individuals 
whose parts of fructification so far differed from the average 
form of the species, that some other insect could serve them 
as pollen-carrier, would be sufficiently prolific to have good 
chances of perpetuating themselves. And on their progeny, 
inheriting the deviation, there would act no external force 
directly calculated to make the deviation greater, and the 
adaptation more complete; since the new circumstances to 
which re-adaptation is required, are such as do not in the 
least alter the equilibrium of functions constituting the life 
of the individual plant. 

§ 162. Among animals, adaptation by direct equilibration 
is similarly traceable, wherever, during the life of the indi- 
vidual, an external change generates some constant or re- 
peated change of function. This is conspicuously the case 
with such parts of an animal as are immediately exposed to 
diffused influences, like those of climate, and with such parts 
of an animal as are occupied in its mechanical actions on the 
environment. Of the one class of cases, the darkening or 
lightening of the skin, that follows exposure to greater or 
less heat, may be taken as an instance ; and with the other 
class of cases, we are made familiar by the increase and de- 
crease which use and disuse cause in the organs of motion 
and manipulation. It is needless here to exemplify these : 
they were treated of in the Second Part of this work. 

But in animals, as in plants, thei^ are many indispensable 


oj£ces fulfilled by parts, between which and the external con- 
ditions they respond to, there is no such action and reaction 
as can directly produce an equilibrium. This is especially 
manifest with dermal appendages. Some ^ound, perhaps, 
exists for the conclusion that the greater or less development 
of hairs, is in part immediately due to increase or decrease of 
demand on their passive function, as non-conductors of heat ; 
but be this as it may, it is impossible that there can exist 
any such cause for those immense developments of hairs which 
we see in the quills of the porcupine, or those complex de- 
velopments of them known as feathers. Such an enamelled 
armour as is worn by the Lepidoateus, is inexplicable as a direct 
result of any functionally- worked change. For purposes of 
defence, such an armour is as needM, or more needftd, for 
hosts of other fishes ; and did it result &om any direct re- 
action of the organism against any offensive actions it was 
subject to, there seems. no reason why other fishes should not 
have developed similar protective coverings. Of 

sundry reproductive appliances, the Uke may be said. The 
secretion of an egg-shell round the substance of an egg, in 
the^viduct of a bird, is quite inexplicable as a consequence 
of some functionally- wrought modification of structure, im- 
mediately caused by some modification of external con- 
ditions. The end ftdfilled by the egg-sheU, is that of 
protecting the contained mass against certain slight pressures 
and collisions, to which it is liable during incubation. How, 
by any process of direct equilibration, could it come to have 
the required thickness? or, indeed, how could it come to 
exist at all? Suppose this protective envelope to be too 
weak, so that some of the eggs a bird lays are broken or 
cracked. In the first place, the breakages or crackings are 
actions of a kind which cannot react on the maternal organ- 
ism, in such way as to cause the secretion of thicker shells 
for the future : to suppose that they can, is to suppose that 
the bird understands the cause of the evil, and that the 
secretion of thicker or thinner shells can be controlled by its 


will. In the second place, such developing chicks as are 
contained in the shells which crack or break, are ..almost 
certain to die; and cannot, therefore, acquire any appro- 
priately-modified constitutions: even supposing any con- 
ceivable relation could be shown, between the impression 
received and the change required. Meanwhile, such eggs as 
escape breakage, are not influenced at all by the require- 
ment ; and hence, on the birds developed from them, there 
cannot have acted any force tending to work the needful 
adjustment of functions. In no way, therefore, can a direct 
equilibration between constitution and conditions be here 
produced. Even in organs that can be modified 

by certain incident forces into correspondence with such 
incident forces, there are some re-adjustments which cannot 
be effected by the direct balancing of inner and outer actions. 
It is thus with the bones. The majority of the bones have 
to resist muscular strains; and it is a familiar fact that 
variations in the muscular strains, call forth, by reaction, 
variations in the strengths of the bones. Here there is 
direct equilibration. But though the greater massiveness 
acquired by bones subject to greater strains, may be ascribed 
to a counter-acting force evoked by a force brought into 
action; it is impossible that the acquirement of greater 
lengths by bones can be thus accounted for. It has been 
supposed that the elongation of the metatarsals in wading 
birds, has resulted from direct adaptation to conditions of 
Ufe. To justify this supposition, however, it must be shown 
that the mechanical actions and reactions in the legs of a 
wading bird, differ from those in the legs of other birds ; 
and that the differential actions are equilibrated by the extra 
lengths. There is not the slightest evidence of this. The 
metatarsals of a bird, have to bear no appreciable strains 
but those due to the superincumbent weight. Standing in 
the water does not appreciably alter these strains ; and even 
if it did, an increase in the lengths of these bones would not 
fit them any better to meet the altered strains. 


§ 163. The conclusion at wliich we arrive is, then, that 
there go on in all organisms, certain changes of ftinction and 
structure that are directly consequent on changes in the 
incident forces — ^inner changes by which the outer changes 
are balanced, and the equilibrium restored. Such re-equi- 
librations, which are often conspicuously exhibited in in- 
dividuals, we have reason to believe continue in successive 
generations ; imtil they are completed by the arrival at 
structures fitted to the modified conditions. But, at the 
same time, we see that the modified conditions to which or- 
ganisms may be adapted by direct equilibration, are con- 
ditions of certain classes only. That a new external action 
may be met by a new internal action, it is needful that it 
shall either continuously or frequently be borne by the in- 
dividuals of the species, without killing or seriously injuring 
them ; and shall act in such way as to afiect th eir functions. 
And we find on examination, that many of the environing 
changes to which organisms have to be adjusted, are not of 
these kinds : being changes which either do not immediately 
affect the functions at all, or else affect them in ways that 
prove fatal. 

Hence there must be at work some other process, which 
equilibrates the actions of organisms with the actions they 
are exposed to. Plants and animals that continue to exist, 
are necessarily plants and animals whose powers balance the 
powers that act on them ; and as their environments 
change, the changes which plants and animals undergo, must 
necessarily be changes towards a re-establishment of the 
balance. Besides direct equilibration, there must therefore 
be an indirect equilibration. How this goes on we have now 
to inquire. 



§ 164. Besides those perturbations produced in the moving 
equilibrium of any organism by special disturbing forces, 
there are ever going on many other perturbations — some 
which are the still-reverberating effects of disturbing forces 
previously experienced by the individual, and others which 
are the still-reverberating effects of disturbing forces expe- 
rienced by ancestral individuals ; and the multiplied devia- 
tions of function so caused, imply multiplied deviations of 
structure. In § 155 there was re-illustrated the truth, set 
forth at length when treating of Adaptation (§ 69), that an 
organism in a state of moving equilibrium, cannot have 
extra function thrown on any organ, and extra growth pro- 
duced in such organ, without there being entailed correlative 
changes throughout all other functions, and eventually 
throughout all other organs. And when treating of Varia- 
tion (§ 90), we saw that individuals which have been made, 
by their different circimistances, to deviate functionally and 
structurally from the average type in different directions, 
will bequeath to their joint offspring, compound perturbations 
of function and compound deviations of structure, endlessly 
varied in their kinds and amounts. That is to say, besides 
the primary perturbations and deviations directly caused in 
organisms by altered actions in their environments, there 
are ever being indirectly caused, secondary and tertiary per- 


turbations and deviations, which, when compounded with one 
another from generation to generation, work innumerable 
slight modifications in the moving equilibria and correlative 
structures throughout the species. 

Now if the individuals of a species are thus necessarily 
made unlike, in countless ways and degrees — ^if the compli- 
cated sets of rhythms which we call their functions, though 
similar in their general characters, are dissimilar in their 
details — if in one individual the amount of action in a par- 
ticular direction is greater than in any other individual, or if 
here a peculiar combination gives a resulting force which is 
not found elsewhere ; then, among all the individuals, some 
will be less liable than others to have their equilibria over- 
thrown by a particular incident force, previously unexperi- 
enced. Unless the change in the environment is of so vio- 
lent a kind as to be imiversally fatal to the species, it must 
affect more or less differently the slightly different moving 
equilibria which the members of the species present. It 
cannot but happen that some will be more stable than others, 
when exposed to this new or altered factor. That is to say, 
it cannot but happen that those individuals whose ftmctions 
are most out of equilibrium with the modified aggregate of 
external forces, wiU be those to die ; and that those will sur- 
vive whose functions happen to be most nearly in equilibrium 
with the modified aggregate of external forces. 

But this survival of the fittest, implies multiplication of 
the fittest. Out of the fittest thus multiplied, there will, as 
before, be an overthrowing of the moving equilibrium wher- 
ever it presents the least opposing force to the new incident 
force. And by the continual destruction of the individuals 
that are the least capable of maintaining their equilibria in 
presence of this new incident force, there must eventually be 
arrived at an altered type completely in equilibrium with the 
altered conditions. 

§ 165. This survival of the fittest, which I have here 


souglit to express in meclianical terms, is that which Mr Dar- 
win has called "natural selection, or the preservation of 
favoured races in the struggle for life." That there is going 
on a process of this kind throughout the organic world, 
Mr Darwin's great work on the Origin of Species has shown 
to the satisfaction of nearly all naturalists. Indeed, when 
once enunciated, the truth of his hypothesis is so obvious as 
scarcely to need proof. Though evidence may be reqidred 
to show that natural selection accoimts for everything ascribed 
to it, yet no evidence is required to show that natural selec- 
tion has always been going on, is going on now, and must 
ever continue to go on. Recognizing this as an d priori cer- 
tainty, let us contemplate it imder its two distinct aspects. 

That organisms which live, thereby prove themselves fit to 
live, in so far as they have been tried ; whiie organisms which 
die, thereby prove themselves in some respects unfitted for 
living ; are facts no less manifest, than is the fact that this 
self-acting purification of a species, must tend ever to insure 
adaptation between it and its environment. This adaptation 
may be either so maintained or so produced. Doubt- 

less many who have looked at Nature with philosophic eyes, 
have observed that death of the worst and multiplication of 
the best, must result in the maintenance of a Constitution 
in harmony with surrounding circumstances. That the aver- 
age vigour of any race would be diminished, did the diseased 
and feeble habitually survive and propagate ; and that the 
destruction of such, through failure to fiilfil some of the con- 
ditions to life, leaves behind those which are able to fulfil the 
conditions to life, and thus keeps up the average fitness to 
the conditions of life ; are almost self-evident truths. But 
to recognize ** natural selection " as a means of preserving 
an already-established balance between the powers of a spe- 
cies and the forces to which it is subject, is to recognize it 
only in its simplest and most general mode of action. It is 
the more special mode of action with which we are here con- 
cerned. This more special mode of action, Mr Dar- 


win has been the first to perceive. To him we owe the dis- 
covery that natural selection is capable of producing fitness 
between organisms and their circumstances ; and he, too, has 
the merit of appreciating the immensely-important conse- 
quences that follow from this. He has worked up an enormous 
mass of evidence into an elaborate demonstration, that this 
" preservation of favotired races in the struggle for life," is 
an ever-acting cause of divergence among organic forms. 
He has traced out the involved results of the process with 
marvellous subtlety. He has shown how hosts of otherwise 
inexplicable facts, are fully accounted for by it. In brief, he 
has proved that the cause he alleges is a true cause ; that it 
is a cause which we see habitually in action ; and that the 
results to be inferred from it, are in harmony with the phe- 
nomena which the Organic Creation presents, both as a whole 
and in its details. Let us glance at a few of the more im- 
portant interpretations which the hypothesis Aimishes. 

A soil possessing some ingredient in unusual quantity, 
may supply to a plant an excess of the matter required for a 
certain class of its tissues ; and may cause all the parts formed 
of such tissues to be abnormally developed. Suppose that 
among these are the hairs clothing its surfaces, including 
those which grow on its seeds. Thus furnished with some- 
what longer fibres, its seeds, when shed, are carried a little 
further by the wind before they fall to the ground. The 
young plants growing up from them, being rather more 
widely dispersed than those produced by other individuals of 
the same species, will be less liable to smother one another ; 
and a greater nimiber may therefore reach maturity and 
fructify. Supposing the next generation subject to the same 
peculiarity of nutrition, some of the seeds borne by its mem- 
bers will not simply inherit this increased development of 
hairs, but will carry it further ; and these, stiU more advan- 
taged in the same way as before, will, on the average, have 
stiU more numerous chances of continuing the race. Thus, 
by the survival, generation after generation, of those possess- 


ing these longer hairs, and the inheritance of successive incre- 
ments of growth in the hairs, there may result a seed deviat- 
ing greatly from the original. Other individuals of the 
same species, subject to the different physical conditions of 
other localities, may develop somewhat thicker or harder 
coatings to their seeds : so rendering their seeds less digest- 
ible by the birds that devour them. Such thicker-coated 
seeds, by escaping undigested more frequently than thinner- 
coated ones, will have additional chances of growing up and 
leaving offspring ; and this process, acting in a cumulative 
manner through successive years, will produce a seed diverg- 
ing in another direction from the ancestral type. Again, 
elsewhere, some modification in the physiologic actions of 
the plant, may lead to an imusual secretion of an essential 
oil in the seeds ; which rendering them unpalatable to crea- 
tures that would otherwise feed on them, may diminish the 
destruction of the seeds, so giving an advantage to the variety 
in its rate of multiplication ; and this incidental peculiarity 
proving a preservative, will, as before, be gradually increased 
by natural selection, until it constitutes another divergence. 
Now in these and countless analogous cases, we see that plants 
may become better adapted, or re-adapted, to the aggregate of 
surroimding agencies, not through any direct action of such 
agencies upon them, but through their indirect action — 
through the destruction by them of the individuals which are 
least congruous with them, and the survival of those which 
are most congruous with them. All these slight variations 
of function and structure, arising among the members of a 
species, serve as so many experiments ; the great majority of 
which fail, but a few of which succeed. Just as we see that 
each plant bears a multitude of seeds, out of which some two or 
three happen to fulfil all the conditions required for reaching 
maturity, and continuing the race ; so we see that each species 
is perpetually producing numerous slightly-modified forms, 
deviating in all directions from the average, out of which 
most fit the surrounding conditions no better than their pa- 


rents, or not so well, but some few of which fit the conditions 
better; and doing so, are enabled the better to preserve them- 
selves, and to produce offspring similarly capable of preserv- 
ing themselves. Among animals the like process re- 
sults in the like development of various structures which 
cannot have been affected by the performance of functions — 
their ftinctions being purely passive. The thick shell of a 
mollusk, is inexplicable as a result of direct reactions of the 
organism against the external actions to which it is exposed ; 
but it is quite explicable as a result of the survival, genera- 
tion after generation, of individuals whose thicker coverings 
protected them against enemies. Similarly with such a 
dermal structure as that of the tortoise. Though we have evi- 
dence that the skin where it is continually exposed to pres- 
sure and friction may thicken, and so re-establish the equi- 
librium, by opposing a greater inner force to a greater outer 
force ; yet we have no evidence that a coat of armour like 
that of the tortoise can be so produced. Nor, indeed, are the 
conditions under which only its production in such a man- 
ner could be accounted for, fulfilled ; since the surface of the 
tortoise is not exposed to greater pressure and friction than 
the surfaces of other creatures. This massive carapace, and 
the strangely-adapted osseous frame-work which supports it, 
are unaccountable as results of evolution, unless through the 
process of natural selection. Thus, too, is it with the pro- 
duction of colours in birds and in insects ; the formation of 
odoriferous glands in mammals ; the growth of such excres- 
cences as those of the camel. Thus, in short, is it with all 
those organs of animals, which do not play active parts in the 
compound rhythms of their functions. 

Besides giving us explanations of structural characters 
that are otherwise unaccountable, Mr Darwin shows how 
natural selection explains peculiar relations between indi- 
viduals in certain species. Such facts as the dimorphism of 
the primrose and other flowers, he proves to be quite in har- 
mony with his hypothesis, though stumbling-blocks to all 


other hypotheses. While the production of neuters among 
bees and' ants, is inexplicable as a result of direct adaptation^ 
natural selection affords a feasible solution of it. The various 
differences that accompany difference of sex> sometimes 
slight, sometimes very great, are similarly accounted for. 
As before suggested (§ 79), natural selection appears capa- 
ble of producing and maintaining the right proportion of 
the sexes in each species ; and it requires but to contemplate 
the bearings of the argument, to see that the formation of 
different sexes may itself have been determined in the sam^ 

To convey here an adequate idea of Mr Darwin's doctrine, 
in the immense range of its applications, is of course impos- 
sible. The few illustrations just given, serving but dimly to 
indicate the many classes of phenomena interpreted by it, 
are set down simply to remind the reader what Mr Darwin's 
hypothesis is, and what are the else insoluble problems which 
it solves for us. 

§ 166. But now, though it seems to me that we are thus 
supplied with a key to phenomena which are multitudinous 
and varied beyond all conception ; it also seems to me that 
there is a moiety of the phenomena which this key will not 
unlock. Mr Darwin himself recognizes use and disuse of 
parts, as causes of modifications in organisms ; and does this, 
indeed, to a greater extent than do some who accept his 
general conclusion. But I conceive that he does not re- 
cognize them to a sufficient extent. While he conclusively 
shows that the inheritance of changes of structure, caused by 
changes of function, is utterly insufficient to explain a great 
mass — probably the greater mass— of morphological pheno- 
mena ; I think he leaves unconsidered a mass of morphological 
phenomena that are explicable as results of functionally- 
acquired modifications, transmitted and increased, and which 
are not explicable as results of natural selection. 

By induction, as weU as by inference from the hypothesis 



of natural selection, we know that there exists a balance 
among the powers of organs which habitually act together — 
such proportions among them, that no one has any consider- 
able excess of efficiency. We see, for example, that through- 
out the vascular system, there is maintained an equilibrium 
between the powers, that is, the developments, of the com- 
ponent parts : in some cases, under excessive exertion, the 
heart gives way, and we have enlargement ; in other cases 
the large arteries give way, and we have aneurisms ; in other 
cases the minute blood-vessels give way — ^now bursting, now 
becoming chronically congested. That is to say, in the 
average constitution, no superfluous strength is possessed 
by any of the appliances for circulating the blood. Take, 
again, a set of motor organs. Great strain here causes the 
fibres of a muscle to tear. There the muscle does not yield 
but the tendon snaps. Elsewhere neither muscle nor tendon 
is damaged, but the bone breaks. Joining with these instances 
the general fact, that under the same adverse conditions, 
different individuals show their slight differences of consti- 
tution by going wrong some in one way and some in an- 
other ; and that even in the same individual, similar adverse 
conditions will now affect one viscus and now another ; it 
becomes manifest that though there cannot be maintaLaed 
an accurate or absolute balance among the powers of the 
organs composing an organism, yet the excesses and de- 
ficiencies of power are extremely slight. That they must be 
extremely slight, is, as before said, a deduction from the 
hypothesis of natural selection. Mr Darwin himself argues 
" that natural selection is continually trying to economize in 
every part of the organization. If imder changed conditions 
of life a structure before useful becomes less useftd, any 
diminution, however slight, in its development, will be seized 
on by natural selection, for it will profit the individual not 
to have its nutriment wasted in building up an useless struc- 
ture." In other words, if any muscle has more fibres than 
can be utilized, or if a bone be stronger than needful, no ad- 


vantage results, but rather a disadvantage — ^a disadvantage 
which will decrease the chances of survival. Hence 

it becomes a corollary, that among any organs which habit- 
ually act in concert, an increase of one can be of no service 
unless there is a concomitant increase of the rest. The co- 
operative parts must vary together ; otherwise variation will 
be detrimental. A stronger muscle must have a stronger bone 
to resist its contractions; must have stronger correlated mus- 
cles and ligaments to secure the neighbouring articulations ; 
must have larger blood-vessels to bring it supplies; must 
have a more massive nerve to bring it stimulus, and some 
extra development of a nerj^ous centre to supply this extra 
stimidus. The question arises, then, — does spontaneous 
variation occur simidtaneously in all these co-operative 
parts P Have we any reason to think that they spontaneously 
increase or decrease together ? The assumption that they 
do, seems to me imtenable ; and its untenability will, I think, 
become conspicuous if we take a case, and observe how ex- 
tremely numerous and involved are the variations which 
must be supposed to occur together. In illustration 

of another point, we have already considered the modifica- 
tion required to accompany increased weight of the head. 
Instead of the bison, however, the moose deer, or the extinct 
Irish elk, will here best serve our purpose. In this species 
the male has enormously-developed horns, which are used for 
purposes of oflfence and defence. These horns, weighing up- 
wards of a himdred- weight, are carried at great mechanical 
disadvantage — supported as they are along with the massive 
skull which bears them, at the extremity of the outstretched 
neck. Further, that these heavy horns may be of use in 
fighting, the supporting bones and muscles must be strong 
enough, not simply to carry them, but to put them in 
motion with the rapidity required for giving blows. Let us, 
then, ask how, by natural selection, this complex apparatus 
of bones and muscles can have been developed, pari passu 
with the horns ? If we suppose the horns to have originally 

29 * 


been of like size with those borne by other kinds of deer ; 
and if we suppose that in certain individuals, they became 
larger by spontaneous variation ; what would be the con- 
comitant changes required to render their greater size use&l ? 
Other things equals the blow given by a larger horn would 
be a blow given by a heavier mass moving at a smaller 
velocity : the momentum would be the same as before ; and 
the area of contact with the body struck being somewhat 
increased, while the velocity was decreased, the injury done 
would be less. That the horns may become better weapons, 
the whole apparatus which moves them must be so strength- 
ened as to impress more force on. them, and to bear the more 
violent reactions of the blows given. The bones of the skull 
on which the horns are seated must be thickened ; otherwise 
they will break. To render the thickening of these bones 
advantageous, the vertebrsB of the neck must be farther de- 
veloped ; and without the ligaments that hold together these 
vertebrae, and the muscles which move them, are also enlarged, 
nothing will be gained. Such modifications of the neck will 
be useless, or rather will be detrimental, if its fulcrum be not 
made capable of resisting intenser strains : the upper dorsal 
vertebrae and their spines must be strengthened, that they 
may withstand the more violent contractions of the neck- 
muscles; and like changes must be made on the scapular 
arch. Still more must there be required a simultaneous de- 
velopment of the bones and muscles of the fore-legs ; since 
each of these extra growths in the horns, in the skull, in the 
neck, in the shoulders, adds to the burden which the fore- 
legs have to bear ; unless this deer with its heavier horns, 
head, neck, and shoulders, had stronger fore-legs, it would 
not only suflFer from loss of speed but would even fail in fight. 
Hence, to